2017 SkS Weekly Climate Change & Global Warming News Roundup #43

A chronological listing of news articles posted on the Skeptical Science Facebook page during the past week. 

Editor's Pick

Coal use must 'pretty much' be gone by 2050 to curb sea-level rise, researchers say

Antarctic Sea Ice 

Warming waters are melting the Antarctic ice sheets from below. Photo: APT

Coal use will have to be "pretty much" gone by mid-century if the planet is to avoid sea-level rise of more than a metre by 2100 as Antarctic ice sheets disintegrate faster than expected, new modelling by an Australian-led team has found.

On business-as-usual projections, sea-level rise by the end of the century could exceed 1.3 metres compared with the 1986-2005 average, or 55 per cent more than predicted in the Fifth Assessment Report by the Intergovernmental Panel on Climate Change, according to research published in the Environmental Research Letters journal.

"We have provided a preview of what will have to be considered and assessed in more detail by the upcoming Sixth IPCC report," due for release in 2021, said Alexander Nauels, lead author of the report, and a researcher at Melbourne University's Australian-German Climate & Energy College. 

Coal use must 'pretty much' be gone by 2050 to curb sea-level rise, researchers say by Peter Hannam, Sydney Morning Herald, Oct 26, 2017

Links posted on Facebook

Sun Oct 22, 2017

Mon Oct 23, 2017

Tue Oct 24, 2017

Wed Oct 25, 2017

Thu Oct 26, 2017

Fri Oct 27, 2017

Sat Oct 28, 2017



from Skeptical Science http://ift.tt/2iEnygN
A chronological listing of news articles posted on the Skeptical Science Facebook page during the past week. 

Editor's Pick

Coal use must 'pretty much' be gone by 2050 to curb sea-level rise, researchers say

Antarctic Sea Ice 

Warming waters are melting the Antarctic ice sheets from below. Photo: APT

Coal use will have to be "pretty much" gone by mid-century if the planet is to avoid sea-level rise of more than a metre by 2100 as Antarctic ice sheets disintegrate faster than expected, new modelling by an Australian-led team has found.

On business-as-usual projections, sea-level rise by the end of the century could exceed 1.3 metres compared with the 1986-2005 average, or 55 per cent more than predicted in the Fifth Assessment Report by the Intergovernmental Panel on Climate Change, according to research published in the Environmental Research Letters journal.

"We have provided a preview of what will have to be considered and assessed in more detail by the upcoming Sixth IPCC report," due for release in 2021, said Alexander Nauels, lead author of the report, and a researcher at Melbourne University's Australian-German Climate & Energy College. 

Coal use must 'pretty much' be gone by 2050 to curb sea-level rise, researchers say by Peter Hannam, Sydney Morning Herald, Oct 26, 2017

Links posted on Facebook

Sun Oct 22, 2017

Mon Oct 23, 2017

Tue Oct 24, 2017

Wed Oct 25, 2017

Thu Oct 26, 2017

Fri Oct 27, 2017

Sat Oct 28, 2017



from Skeptical Science http://ift.tt/2iEnygN
Aucun commentaire:
Libellés : ,

Misty moon over North Borneo

Photo via Jenney Disimon.

The moon was 56.2% illuminated at 9.30pm on October 28, 2017.

.



from EarthSky http://ift.tt/2ySgV0P

Photo via Jenney Disimon.

The moon was 56.2% illuminated at 9.30pm on October 28, 2017.

.



from EarthSky http://ift.tt/2ySgV0P
Aucun commentaire:
Libellés :

Did Ceres once have an ocean?

Left, Ceres as seen by NASA’s Dawn spacecraft from its high-altitude mapping orbit at 913 miles (1,470 km) above the surface. Right, a map showing variations in Ceres’ gravity field as measured by the Dawn spacecraft. This gravity map supports the idea of an ancient ocean on Ceres. Image via NASA JPL.

Ceres – orbiting between Mars and Jupiter – was classified as a planet when it was first discovered in 1801, until the 1850s when it became known as the largest of the little worlds in the asteroid belt. In 2006, astronomers re-classified it as a dwarf planet. Still, it may seem odd to you to imagine little Ceres, a world only 590 miles (950 km) across, having an ocean. And yet Ceres is known to have water-containing minerals on its surface. Two recent studies explore the possibility of an ocean on Ceres in the distant past, and they shed light on the question of what happened to this ocean, if it existed, and on whether Ceres might still have liquid water today.

Our knowledge of Ceres has vastly increased in the past couple of years, since the Dawn spacecraft began orbiting it in early 2015. Dawn’s mission was recently extended, by the way. NASA said:

The Dawn team found that Ceres’ crust is a mixture of ice, salts and hydrated materials that were subjected to past and possibly recent geologic activity, and that this crust represents most of [an] ancient ocean. The second study builds off the first and suggests there is a softer, easily deformable layer beneath Ceres’ rigid surface crust, which could be the signature of residual liquid left over from the ocean, too.

Julie Castillo-Rogez, Dawn project scientist and co-author of the studies, based at NASA’s Jet Propulsion Laboratory, Pasadena, California, said:

More and more, we are learning that Ceres is a complex, dynamic world that may have hosted a lot of liquid water in the past, and may still have some underground.

Earth-Ceres size comparison. Ceres is little, but it accounts for approximately 1/3 of the mass of the asteroid belt. In 2006, IAU astronomers briefly considered changing the status of Ceres back to that of a major planet, but then opted to make both Ceres and Pluto dwarf planets. The reason is neither Ceres nor Pluto “dominates its orbit.” Both share their orbits with many other smaller bodies, in the case of Ceres, asteroids in what we call the asteroid belt. Image via ThePlanets.org.

Anton Ermakov, a postdoctoral researcher at JPL, led the first study, which is an analysis of measurements made via the Dawn spacecraft of Ceres’ gravity. Such measurements enable scientists to estimate the composition and interior structure of a world like Ceres. This study is published in the peer-reviewed Journal of Geophysical Research. The measurements came from observing the spacecraft’s motions with NASA’s Deep Space Network. The scientists were looking small changes in the spacecraft’s orbit, which indicate gravity anomalies. NASA said:

Three craters — Occator, Kerwan and Yalode — and Ceres’ solitary tall mountain, Ahuna Mons, are all associated with ‘gravity anomalies.’ This means discrepancies between the scientists’ models of Ceres’ gravity and what Dawn observed in these four locations can be associated with subsurface structures …

[Ermakov’s study also found] the crust’s density to be relatively low, closer to that of ice than rocks. However, a study by Dawn guest investigator Michael Bland of the U.S. Geological Survey indicated that ice is too soft to be the dominant component of Ceres’ strong crust. So, how can Ceres’ crust be as light as ice in terms of density, but simultaneously much stronger? To answer this question, another team modeled how Ceres’ surface evolved with time.

Ahuna Mons on Ceres, a mountain about 4 miles (6 km) tall, in a simulated view using NASA’s Dawn spacecraft images. This region on Ceres is associated with gravity anomalies, which helps scientists probe Ceres’ interior structure. Image via NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

Roger Fu at Harvard University in Cambridge, Massachusetts, led this second study, which is published in the peer-reviewed journal Earth and Planetary Science Letters. It investigated the strength and composition of Ceres’ crust and deeper interior by studying the dwarf planet’s topography. NASA explained:

By studying how topography evolves on a planetary body, scientists can understand the composition of its interior. A strong, rock-dominated crust can remain unchanged over the 4.5-billion-year-old age of the solar system, while a weak crust rich in ices and salts would deform over that time.

By modeling how Ceres’ crust flows, Fu and colleagues found it is likely a mixture of ice, salts, rock and an additional component believed to be clathrate hydrate. A clathrate hydrate is a cage of water molecules surrounding a gas molecule. This structure is 100 to 1,000 times stronger than water ice, despite having nearly the same density.

The researchers believe Ceres once had more pronounced surface features, but they have smoothed out over time. This type of flattening of mountains and valleys requires a high-strength crust resting on a more deformable layer, which Fu and colleagues interpret to contain a little bit of liquid.

The team thinks most of Ceres’ ancient ocean is now frozen and bound up in the crust, remaining in the form of ice, clathrate hydrates and salts. It has mostly been that way for more than 4 billion years. But if there is residual liquid underneath, that ocean is not yet entirely frozen.

This is consistent with several thermal evolution models of Ceres published prior to Dawn’s arrival there, supporting the idea that Ceres’ deeper interior contains liquid left over from its ancient ocean.

Artist’s concept of Dawn spacecraft orbiting Ceres. Our knowledge of this little world has greatly increased, thanks to Dawn, whose mission was recently extended. Yet mysteries remain. Image via NASA/JPL-Caltech.

Bottom line: Two recent studies explore the possibility of an ocean on Ceres in the distant past, and they shed light on the question of what happened to this ocean, if it existed, and on whether Ceres might still have liquid water today.

Via NASA JPL



from EarthSky http://ift.tt/2gQPRIl

Left, Ceres as seen by NASA’s Dawn spacecraft from its high-altitude mapping orbit at 913 miles (1,470 km) above the surface. Right, a map showing variations in Ceres’ gravity field as measured by the Dawn spacecraft. This gravity map supports the idea of an ancient ocean on Ceres. Image via NASA JPL.

Ceres – orbiting between Mars and Jupiter – was classified as a planet when it was first discovered in 1801, until the 1850s when it became known as the largest of the little worlds in the asteroid belt. In 2006, astronomers re-classified it as a dwarf planet. Still, it may seem odd to you to imagine little Ceres, a world only 590 miles (950 km) across, having an ocean. And yet Ceres is known to have water-containing minerals on its surface. Two recent studies explore the possibility of an ocean on Ceres in the distant past, and they shed light on the question of what happened to this ocean, if it existed, and on whether Ceres might still have liquid water today.

Our knowledge of Ceres has vastly increased in the past couple of years, since the Dawn spacecraft began orbiting it in early 2015. Dawn’s mission was recently extended, by the way. NASA said:

The Dawn team found that Ceres’ crust is a mixture of ice, salts and hydrated materials that were subjected to past and possibly recent geologic activity, and that this crust represents most of [an] ancient ocean. The second study builds off the first and suggests there is a softer, easily deformable layer beneath Ceres’ rigid surface crust, which could be the signature of residual liquid left over from the ocean, too.

Julie Castillo-Rogez, Dawn project scientist and co-author of the studies, based at NASA’s Jet Propulsion Laboratory, Pasadena, California, said:

More and more, we are learning that Ceres is a complex, dynamic world that may have hosted a lot of liquid water in the past, and may still have some underground.

Earth-Ceres size comparison. Ceres is little, but it accounts for approximately 1/3 of the mass of the asteroid belt. In 2006, IAU astronomers briefly considered changing the status of Ceres back to that of a major planet, but then opted to make both Ceres and Pluto dwarf planets. The reason is neither Ceres nor Pluto “dominates its orbit.” Both share their orbits with many other smaller bodies, in the case of Ceres, asteroids in what we call the asteroid belt. Image via ThePlanets.org.

Anton Ermakov, a postdoctoral researcher at JPL, led the first study, which is an analysis of measurements made via the Dawn spacecraft of Ceres’ gravity. Such measurements enable scientists to estimate the composition and interior structure of a world like Ceres. This study is published in the peer-reviewed Journal of Geophysical Research. The measurements came from observing the spacecraft’s motions with NASA’s Deep Space Network. The scientists were looking small changes in the spacecraft’s orbit, which indicate gravity anomalies. NASA said:

Three craters — Occator, Kerwan and Yalode — and Ceres’ solitary tall mountain, Ahuna Mons, are all associated with ‘gravity anomalies.’ This means discrepancies between the scientists’ models of Ceres’ gravity and what Dawn observed in these four locations can be associated with subsurface structures …

[Ermakov’s study also found] the crust’s density to be relatively low, closer to that of ice than rocks. However, a study by Dawn guest investigator Michael Bland of the U.S. Geological Survey indicated that ice is too soft to be the dominant component of Ceres’ strong crust. So, how can Ceres’ crust be as light as ice in terms of density, but simultaneously much stronger? To answer this question, another team modeled how Ceres’ surface evolved with time.

Ahuna Mons on Ceres, a mountain about 4 miles (6 km) tall, in a simulated view using NASA’s Dawn spacecraft images. This region on Ceres is associated with gravity anomalies, which helps scientists probe Ceres’ interior structure. Image via NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

Roger Fu at Harvard University in Cambridge, Massachusetts, led this second study, which is published in the peer-reviewed journal Earth and Planetary Science Letters. It investigated the strength and composition of Ceres’ crust and deeper interior by studying the dwarf planet’s topography. NASA explained:

By studying how topography evolves on a planetary body, scientists can understand the composition of its interior. A strong, rock-dominated crust can remain unchanged over the 4.5-billion-year-old age of the solar system, while a weak crust rich in ices and salts would deform over that time.

By modeling how Ceres’ crust flows, Fu and colleagues found it is likely a mixture of ice, salts, rock and an additional component believed to be clathrate hydrate. A clathrate hydrate is a cage of water molecules surrounding a gas molecule. This structure is 100 to 1,000 times stronger than water ice, despite having nearly the same density.

The researchers believe Ceres once had more pronounced surface features, but they have smoothed out over time. This type of flattening of mountains and valleys requires a high-strength crust resting on a more deformable layer, which Fu and colleagues interpret to contain a little bit of liquid.

The team thinks most of Ceres’ ancient ocean is now frozen and bound up in the crust, remaining in the form of ice, clathrate hydrates and salts. It has mostly been that way for more than 4 billion years. But if there is residual liquid underneath, that ocean is not yet entirely frozen.

This is consistent with several thermal evolution models of Ceres published prior to Dawn’s arrival there, supporting the idea that Ceres’ deeper interior contains liquid left over from its ancient ocean.

Artist’s concept of Dawn spacecraft orbiting Ceres. Our knowledge of this little world has greatly increased, thanks to Dawn, whose mission was recently extended. Yet mysteries remain. Image via NASA/JPL-Caltech.

Bottom line: Two recent studies explore the possibility of an ocean on Ceres in the distant past, and they shed light on the question of what happened to this ocean, if it existed, and on whether Ceres might still have liquid water today.

Via NASA JPL



from EarthSky http://ift.tt/2gQPRIl
Aucun commentaire:
Libellés :

Interpreting the Paris Agreement’s 1.5C temperature limit

This is a re-post from Carbon Brief

Dr Joeri Rogelj is a research scholar at the International Institute for Applied Systems Analysis (IIASA) in Austria, and a coordinating lead author of the IPCC’s Special Report on 1.5C. Dr Carl-Friedrich Schleussner is head of climate science and impacts at Climate Analytics, and is on the steering committee of the initiative Half a degree Additional warming, Prognosis and Projected Impacts (HAPPI).

Long-term temperature limits like 2C or 1.5C above pre-industrial levels have long been used as goalposts for climate change mitigation.

Recently, these limits have received renewed attention in the scientific community, media and general public because of their inclusion in the Paris Agreement and the decision of the Intergovernmental Panel on Climate Change (IPCC) to prepare a Special Report on 1.5C.

However, the Paris Agreement itself does not spell out explicitly how such temperature limits should be used in climate policy and practice. These limits are therefore subject to interpretation, leading to confusion when trying to communicate how achievable the 1.5C limit is and the mitigation effort required.

In a commentary paper for the journal Geophysical Research Letters, we show that the temperature limits in the Paris Agreement should be understood as changes in long-term global averages attributed to human activity, which exclude natural variability.

This means 1.5C might be breached in individual years well before the global long-term 1.5C temperature limit has definitively been crossed.

Long-term goal

The long-term temperature goal agreed in Paris in December 2015 is enshrined in Article 2.1 of the final text. It outlines the aim to hold rising temperatures to “well below 2C above pre-industrial levels” while “pursuing efforts” towards the more ambitious limit of 1.5C.

The Paris Agreement final text. Source: UNFCCC (pdf)

The wording of the text is not without ambiguity (though this was arguably intentional in order to help reach agreement during negotiations). The agreement does not establish two “either-or” temperature goals, but a single goal, yet it does not make explicit how “well below 2C” or “limit to 1.5C” should be interpreted.

In the months since Paris there has been flurry of new journal papers and media articles focusing on the long-term goal – particularly the 1.5C limit – and this has highlighted the different ways in which it is being understood.

Much of the recent peer-reviewed research into 1.5C and 2C has taken the Paris Agreement temperature limits as long-term climatological global averages over multiple decades (see: here, here or here).

In others, the 1.5C and 2C limits have been compared to temperature metrics that look at smaller geographical scales or shorter time periods. These include, for example, looking at land temperatures only or at regional temperatures, or by assessing annual temperatures that include modes of natural variability such as the Pacific Interdecadal Oscillation.

Media articles have also discussed how close record monthly temperatures have come to hitting 1.5C above average.

These widely-different interpretations lead to quite different messages and insights, and have the potential to create confusion around what the long-term goal means and our chances of meeting the challenge.

Thought experiment

So, does it matter if the long-term goal is characterised in different ways? The simple answer is yes.

Widely-different interpretations lead to quite different messages and insights, and have the potential to create confusion around what the long-term goal means and our chances of meeting the challenge.

We illustrate this here with a thought experiment by showing how different warming limit interpretations affect the carbon budget for keeping to the 1.5C limit.

(We argue that one misinterpretation of international climate limits is to assume that they apply to global mean temperature rise including interannual natural variability. This is not the case – as will become clear further below – but let’s make this assumption for our thought experiment.)

Even in a stable climate, annual temperatures fluctuate around a long-term global temperature as a result of natural variability, caused by a range of unforced climate phenomena such as the El Niño-Southern Oscillation, and of variations in natural forcing, including volcanic eruptions, and variations in solar activity.

In a world where human-caused greenhouse gas emissions have taken long-term global warming to 1.5C, there would be a 50:50 chance of annual temperatures in any given year showing more than 1.5C of warming. In other words, you would expect to see more than 1.5C of warming one out of every two years on average over a sustained period of time.

Diverging interpretations of international warming limits, which look at exceeding 1.5C less frequently in individual years, make the challenge of keeping warming below 1.5C much greater.

In our thought experiment, we explore what happens when we reduce the chances of crossing 1.5C in any given year from one in two down to one in five, one in 10, one in 20, or never. The last of these levels, for example, means global temperature virtuallynever passes 1.5C of warming.

For this we derive annual average temperatures for each annual exceedance frequency using simulations from 24 climate models. You can see the results in the chart below, which shows the likely spread of annual temperatures as a result of natural variability.

So, for example, if we were to interpret the 1.5C limit as exceeding 1.5C of warming once every five years, we would actually need to hold the long-term global averagetemperature to 1.41C.

The more strictly we take the 1.5C goal, the lower the long-term average needs to be.

If we want to ensure annual global temperature never exceeds 1.5C of warming (see blue curve on the chart), we actually have to hold the long-term temperature to around 1C – a threshold we have almost reached.

Annual global average temperature anomalies from running a 21-year average for 24 climate models and the 1900-2090 period

Annual global average temperature anomalies from running a 21-year average for 24 climate models and the 1900-2090 period (combined historical and RCP2.6 scenario). Levels shown for four probabilities relating to the 1.5C limit, with the central bold line of each curve showing the equivalent average long-term temperature. Note: this is an approximation of natural variability, as it does not capture low frequency variability, and it also includes variations due to changes in historical natural solar and volcanic forcing. Credit: Joeri Rogelj.

Carbon budgets

Long-term temperature levels, such as those laid down in the Paris Agreement, provide guidance for short, mid and long-term global mitigation action.

One way they are used is by being translated into specific “carbon budgets” – this is the maximum amount of CO2 humans can emit while still having a good chance of meeting a given temperature limit.

Different interpretations of the long-term goal thus affect the carbon budget for 1.5C.

For example, if annual temperatures can only exceed a long-term temperature limit once every five years, the compatible carbon budget is around 200bn tonnes of CO2 smaller than the budget for once every two years. At current CO2 emission rates, that translates into using up the 1.5C budget around five years earlier.

For 1.5C never to be breached in any given year, the carbon budget would be reduced by more than 1,000bn tonnes of CO2.

This shows that there are substantial real-world policy differences involved in the interpretation of the Paris Agreement’s long-term temperature goal.

Our findings for each annual exceedance frequency are shown in the table below.

Implications of limits to the annual exceedance frequency of 1.5C for equivalent long-term global warming levels and respective carbon budgets, based on a transient climate response of 1.65C per 3664bn tonnes of CO2 (which is the average of the IPCC AR5’s likely 0.8 to 2.5C range). This estimate assumes invariable non-CO2 contributions. Reproduced from Rogelj et al. (2017). Note: the cumulative carbon budget for limiting warming to 1.5C relative to 1861-1880 in 50% of the model simulations was reported to be of the order of 2300bn tonnes of CO2 since 1870 in the IPCC Synthesis Report. A recent study, which has also been extensively covered on Carbon Brief and elsewhere online, reported updated estimates for an additional 0.6C of warming above the 2010-2019 average of about 730-880bn tonnes of CO2.

Legal and policy context

So, how can we know the correct way to interpret Paris Agreement temperature levels?

In our article, we show that the answer lies in analysis of the available information and examination of the context – in this case the legal framework of the United Nations Framework Convention on Climate Change (UNFCCC).

The United Nations Framework Convention on Climate Change (UNFCCC) – to which the Paris Agreement is a subsidiary legal instrument – defines “climate change” specifically as changes caused by human activity, without natural variability included.

UN Framework Convention on Climate Change (1992). Source: UNFCCC (pdf)

Further, the most recent IPCC assessment report provides additional clarity by defining “climate” as the statistical description in terms of the average and variability of relevant quantities over a period of time – with a classical period for averaging being 30 years, also commonly used by the World Meteorological Organisation (WMO).

In the context of the Paris Agreement, definitions set out by the UNFCCC will apply. In addition, IPCC assessment reports – particularly the most recent one – played a predominant role defining and underpinning the scientific components of the agreement.

Therefore, we argue that the long-term temperature goal in the Paris Agreement should be understood as long-term changes in climatological averages attributed to human activity – excluding natural variability.

Communicating 1.5C – the challenges ahead

Given the sensitive nature of the topic in the public debate, we think it is indispensable for the scientific community working on the topic to be well aware of the legal and scientific characteristics of the Paris Agreement long-term temperature goal.

At some point in the near future we will record the first year where the global average temperature is 1.5C warmer than pre-industrial levels. This will undoubtedly generate headlines.

Indeed, even before that, we will likely also see individual months and regions “exceeding” 1.5C.

But this won’t necessarily mean we’ve reached 1.5C of human-caused warming because a single month or year is also subject to natural variability. We need to be clear, for example, that even if a year sees 1.5C of warming, it need not mean that we have failed to fulfill the Paris Agreement – although it will provide an important warning shot.

While there are many challenges for scientists and policymakers in how we communicate climate change, being consistent about what the Paris Agreement temperature goal refers to should not be one of them. It is an essential step for providing relevant information to the public and policy debate alike.



from Skeptical Science http://ift.tt/2ySsLFO

This is a re-post from Carbon Brief

Dr Joeri Rogelj is a research scholar at the International Institute for Applied Systems Analysis (IIASA) in Austria, and a coordinating lead author of the IPCC’s Special Report on 1.5C. Dr Carl-Friedrich Schleussner is head of climate science and impacts at Climate Analytics, and is on the steering committee of the initiative Half a degree Additional warming, Prognosis and Projected Impacts (HAPPI).

Long-term temperature limits like 2C or 1.5C above pre-industrial levels have long been used as goalposts for climate change mitigation.

Recently, these limits have received renewed attention in the scientific community, media and general public because of their inclusion in the Paris Agreement and the decision of the Intergovernmental Panel on Climate Change (IPCC) to prepare a Special Report on 1.5C.

However, the Paris Agreement itself does not spell out explicitly how such temperature limits should be used in climate policy and practice. These limits are therefore subject to interpretation, leading to confusion when trying to communicate how achievable the 1.5C limit is and the mitigation effort required.

In a commentary paper for the journal Geophysical Research Letters, we show that the temperature limits in the Paris Agreement should be understood as changes in long-term global averages attributed to human activity, which exclude natural variability.

This means 1.5C might be breached in individual years well before the global long-term 1.5C temperature limit has definitively been crossed.

Long-term goal

The long-term temperature goal agreed in Paris in December 2015 is enshrined in Article 2.1 of the final text. It outlines the aim to hold rising temperatures to “well below 2C above pre-industrial levels” while “pursuing efforts” towards the more ambitious limit of 1.5C.

The Paris Agreement final text. Source: UNFCCC (pdf)

The wording of the text is not without ambiguity (though this was arguably intentional in order to help reach agreement during negotiations). The agreement does not establish two “either-or” temperature goals, but a single goal, yet it does not make explicit how “well below 2C” or “limit to 1.5C” should be interpreted.

In the months since Paris there has been flurry of new journal papers and media articles focusing on the long-term goal – particularly the 1.5C limit – and this has highlighted the different ways in which it is being understood.

Much of the recent peer-reviewed research into 1.5C and 2C has taken the Paris Agreement temperature limits as long-term climatological global averages over multiple decades (see: here, here or here).

In others, the 1.5C and 2C limits have been compared to temperature metrics that look at smaller geographical scales or shorter time periods. These include, for example, looking at land temperatures only or at regional temperatures, or by assessing annual temperatures that include modes of natural variability such as the Pacific Interdecadal Oscillation.

Media articles have also discussed how close record monthly temperatures have come to hitting 1.5C above average.

These widely-different interpretations lead to quite different messages and insights, and have the potential to create confusion around what the long-term goal means and our chances of meeting the challenge.

Thought experiment

So, does it matter if the long-term goal is characterised in different ways? The simple answer is yes.

Widely-different interpretations lead to quite different messages and insights, and have the potential to create confusion around what the long-term goal means and our chances of meeting the challenge.

We illustrate this here with a thought experiment by showing how different warming limit interpretations affect the carbon budget for keeping to the 1.5C limit.

(We argue that one misinterpretation of international climate limits is to assume that they apply to global mean temperature rise including interannual natural variability. This is not the case – as will become clear further below – but let’s make this assumption for our thought experiment.)

Even in a stable climate, annual temperatures fluctuate around a long-term global temperature as a result of natural variability, caused by a range of unforced climate phenomena such as the El Niño-Southern Oscillation, and of variations in natural forcing, including volcanic eruptions, and variations in solar activity.

In a world where human-caused greenhouse gas emissions have taken long-term global warming to 1.5C, there would be a 50:50 chance of annual temperatures in any given year showing more than 1.5C of warming. In other words, you would expect to see more than 1.5C of warming one out of every two years on average over a sustained period of time.

Diverging interpretations of international warming limits, which look at exceeding 1.5C less frequently in individual years, make the challenge of keeping warming below 1.5C much greater.

In our thought experiment, we explore what happens when we reduce the chances of crossing 1.5C in any given year from one in two down to one in five, one in 10, one in 20, or never. The last of these levels, for example, means global temperature virtuallynever passes 1.5C of warming.

For this we derive annual average temperatures for each annual exceedance frequency using simulations from 24 climate models. You can see the results in the chart below, which shows the likely spread of annual temperatures as a result of natural variability.

So, for example, if we were to interpret the 1.5C limit as exceeding 1.5C of warming once every five years, we would actually need to hold the long-term global averagetemperature to 1.41C.

The more strictly we take the 1.5C goal, the lower the long-term average needs to be.

If we want to ensure annual global temperature never exceeds 1.5C of warming (see blue curve on the chart), we actually have to hold the long-term temperature to around 1C – a threshold we have almost reached.

Annual global average temperature anomalies from running a 21-year average for 24 climate models and the 1900-2090 period

Annual global average temperature anomalies from running a 21-year average for 24 climate models and the 1900-2090 period (combined historical and RCP2.6 scenario). Levels shown for four probabilities relating to the 1.5C limit, with the central bold line of each curve showing the equivalent average long-term temperature. Note: this is an approximation of natural variability, as it does not capture low frequency variability, and it also includes variations due to changes in historical natural solar and volcanic forcing. Credit: Joeri Rogelj.

Carbon budgets

Long-term temperature levels, such as those laid down in the Paris Agreement, provide guidance for short, mid and long-term global mitigation action.

One way they are used is by being translated into specific “carbon budgets” – this is the maximum amount of CO2 humans can emit while still having a good chance of meeting a given temperature limit.

Different interpretations of the long-term goal thus affect the carbon budget for 1.5C.

For example, if annual temperatures can only exceed a long-term temperature limit once every five years, the compatible carbon budget is around 200bn tonnes of CO2 smaller than the budget for once every two years. At current CO2 emission rates, that translates into using up the 1.5C budget around five years earlier.

For 1.5C never to be breached in any given year, the carbon budget would be reduced by more than 1,000bn tonnes of CO2.

This shows that there are substantial real-world policy differences involved in the interpretation of the Paris Agreement’s long-term temperature goal.

Our findings for each annual exceedance frequency are shown in the table below.

Implications of limits to the annual exceedance frequency of 1.5C for equivalent long-term global warming levels and respective carbon budgets, based on a transient climate response of 1.65C per 3664bn tonnes of CO2 (which is the average of the IPCC AR5’s likely 0.8 to 2.5C range). This estimate assumes invariable non-CO2 contributions. Reproduced from Rogelj et al. (2017). Note: the cumulative carbon budget for limiting warming to 1.5C relative to 1861-1880 in 50% of the model simulations was reported to be of the order of 2300bn tonnes of CO2 since 1870 in the IPCC Synthesis Report. A recent study, which has also been extensively covered on Carbon Brief and elsewhere online, reported updated estimates for an additional 0.6C of warming above the 2010-2019 average of about 730-880bn tonnes of CO2.

Legal and policy context

So, how can we know the correct way to interpret Paris Agreement temperature levels?

In our article, we show that the answer lies in analysis of the available information and examination of the context – in this case the legal framework of the United Nations Framework Convention on Climate Change (UNFCCC).

The United Nations Framework Convention on Climate Change (UNFCCC) – to which the Paris Agreement is a subsidiary legal instrument – defines “climate change” specifically as changes caused by human activity, without natural variability included.

UN Framework Convention on Climate Change (1992). Source: UNFCCC (pdf)

Further, the most recent IPCC assessment report provides additional clarity by defining “climate” as the statistical description in terms of the average and variability of relevant quantities over a period of time – with a classical period for averaging being 30 years, also commonly used by the World Meteorological Organisation (WMO).

In the context of the Paris Agreement, definitions set out by the UNFCCC will apply. In addition, IPCC assessment reports – particularly the most recent one – played a predominant role defining and underpinning the scientific components of the agreement.

Therefore, we argue that the long-term temperature goal in the Paris Agreement should be understood as long-term changes in climatological averages attributed to human activity – excluding natural variability.

Communicating 1.5C – the challenges ahead

Given the sensitive nature of the topic in the public debate, we think it is indispensable for the scientific community working on the topic to be well aware of the legal and scientific characteristics of the Paris Agreement long-term temperature goal.

At some point in the near future we will record the first year where the global average temperature is 1.5C warmer than pre-industrial levels. This will undoubtedly generate headlines.

Indeed, even before that, we will likely also see individual months and regions “exceeding” 1.5C.

But this won’t necessarily mean we’ve reached 1.5C of human-caused warming because a single month or year is also subject to natural variability. We need to be clear, for example, that even if a year sees 1.5C of warming, it need not mean that we have failed to fulfill the Paris Agreement – although it will provide an important warning shot.

While there are many challenges for scientists and policymakers in how we communicate climate change, being consistent about what the Paris Agreement temperature goal refers to should not be one of them. It is an essential step for providing relevant information to the public and policy debate alike.



from Skeptical Science http://ift.tt/2ySsLFO
Aucun commentaire:
Libellés : ,

Wayward moon receding from Earth

Above: Simulated image of the waxing gibbous moon of October 28, 2017 via the U.S. Naval Observatory.

From 1969 to 1972, Apollo astronauts had left laser reflectors on the moon’s surface, enabling astronomers to measure the moon’s distance from Earth with great accuracy. Although the moon’s distance from earth varies each month because of its eccentric orbit, the moon’s mean distance from Earth is nonetheless increasing at the rate of about 3.8 centimeters (1.5 inches) per year. That’s about the rate that fingernails grow.

Tidal friction with the Earth’s oceans is responsible for this long-term increase of the moon’s distance from Earth. It’s causing the moon to spiral into a more distant orbit. Tidal friction also slows down the Earth’s rotation, lengthening the day by about 1 second every 40,000 years. Hence, the number of days in a year is slowly diminishing over the long course of time.

Simulations suggest that at the time of the moon’s formation some 4.5 billion years ago, the moon was only about 20,000 to 30,000 kilometers (12,000 to 18,000 miles) from Earth. Way back then, Earth’s day might have been only 5 or 6 hours long. That would mean over 1,400 days in one year!

View larger. The Apollo 11 lunar laser ranging retroreflector array via NASA.

View larger. | The Apollo 11 lunar laser ranging retroreflector array on the moon via NASA.

However, astronomers suspected the moon was receding from Earth before the heyday of the Apollo astronauts. Edmund Halley’s (1656 to 1741) studies of ancient solar and lunar eclipses suggested the possibility, as well. George Howard Darwin (1845 to 1912) is credited for figuring out mathematically how tidal friction affects the moon’s orbit.

Studies in fossilized coral indicate that the Earth had spun faster upon its rotational axis when the moon was closer to Earth. Millions of years ago, days on Earth were shorter yet more abundant. For instance, around 900 million years ago, there were about 480 18-hours days in one year. Around 400 million years ago, there were about 400 22-hour days in one year. Looking into the future, astronomers expect longer days but fewer of them in one year.

If the lifetime of the Earth-moon system lasts long enough (which is doubtful), it is projected that after many billions of years, the same sides of the Earth and moon would face one another. In other words, the Earth’s rotational period and the moon’s orbital period would equal one another, representing a period of 47 days. At that time, the Earth/moon distance would expand to some 336,000 miles or 560,000 km, exceeding the present distance of 238,855 miles or 384,400 km by nearly 150%.

As you view our companion world tonight, ponder on the rich history and intriguing future of our planet Earth and its wayward moon!



from EarthSky http://ift.tt/2yXXfIO

Above: Simulated image of the waxing gibbous moon of October 28, 2017 via the U.S. Naval Observatory.

From 1969 to 1972, Apollo astronauts had left laser reflectors on the moon’s surface, enabling astronomers to measure the moon’s distance from Earth with great accuracy. Although the moon’s distance from earth varies each month because of its eccentric orbit, the moon’s mean distance from Earth is nonetheless increasing at the rate of about 3.8 centimeters (1.5 inches) per year. That’s about the rate that fingernails grow.

Tidal friction with the Earth’s oceans is responsible for this long-term increase of the moon’s distance from Earth. It’s causing the moon to spiral into a more distant orbit. Tidal friction also slows down the Earth’s rotation, lengthening the day by about 1 second every 40,000 years. Hence, the number of days in a year is slowly diminishing over the long course of time.

Simulations suggest that at the time of the moon’s formation some 4.5 billion years ago, the moon was only about 20,000 to 30,000 kilometers (12,000 to 18,000 miles) from Earth. Way back then, Earth’s day might have been only 5 or 6 hours long. That would mean over 1,400 days in one year!

View larger. The Apollo 11 lunar laser ranging retroreflector array via NASA.

View larger. | The Apollo 11 lunar laser ranging retroreflector array on the moon via NASA.

However, astronomers suspected the moon was receding from Earth before the heyday of the Apollo astronauts. Edmund Halley’s (1656 to 1741) studies of ancient solar and lunar eclipses suggested the possibility, as well. George Howard Darwin (1845 to 1912) is credited for figuring out mathematically how tidal friction affects the moon’s orbit.

Studies in fossilized coral indicate that the Earth had spun faster upon its rotational axis when the moon was closer to Earth. Millions of years ago, days on Earth were shorter yet more abundant. For instance, around 900 million years ago, there were about 480 18-hours days in one year. Around 400 million years ago, there were about 400 22-hour days in one year. Looking into the future, astronomers expect longer days but fewer of them in one year.

If the lifetime of the Earth-moon system lasts long enough (which is doubtful), it is projected that after many billions of years, the same sides of the Earth and moon would face one another. In other words, the Earth’s rotational period and the moon’s orbital period would equal one another, representing a period of 47 days. At that time, the Earth/moon distance would expand to some 336,000 miles or 560,000 km, exceeding the present distance of 238,855 miles or 384,400 km by nearly 150%.

As you view our companion world tonight, ponder on the rich history and intriguing future of our planet Earth and its wayward moon!



from EarthSky http://ift.tt/2yXXfIO
Aucun commentaire:
Libellés :

News digest – e-cig inquiry, breast cancer risk, junk food promotions, and… a lack of goodwill?

This week we reported that MPs have launched an inquiry into e-cigarettes. The House of Commons Science and Technology Select Committee wants to find out what evidence is missing around e-cigs and their health effects. Public Health England estimates that e-cigarettes are far safer than tobacco, but other countries have taken different approaches. BBC News has more.

Cancer patients are less likely to have chemotherapy if diagnosed early, reports the Huffington Post. The new data report shows that patients whose cancer was diagnosed early were more likely to have surgery than chemo or radiotherapy. Our blog post has more.

We covered a small study that found the most aggressive type of ovarian cancer develops from cells that come from the fallopian tubes rather than the ovaries. Until recently it was thought that the disease developed from cells lining the surface of the ovary, but the new work could lead to new ways to prevent and treat it. The Independent also had this story.

Number of the week

65

New genetic variants found to increase the risk of breast cancer by a small amount

Junk food promotions in Scotland will be restricted under plans reported by BBC News. The Scottish government wants to limit deals on foods high in fat, sugar and salt, and could push for powers to ban TV adverts for unhealthy foods before the 9pm watershed. The Herald and iNews also had the story.

New DNA changes that increase the risk of breast cancer by a small amount have been identified, reports the Guardian. These 65 new variants, combined with the 180 already known, account for around a fifth of the increased risk that comes from inheriting the faulty genes. The Independent also covered this story.

Different types of brain tumours may share similar survival strategies, reports Medical Xpress. Surprisingly, a new study found the way cells from different kinds of brain tumour generate and use energy is similar, opening up new treatment research avenues. Check out our blog post for more.

An experimental gene therapy has shown promise for treating some brain tumour patients. We reported on a small clinical trial that found the therapy to be safe in patients with a kind of tumour called glioma, and the researchers will now see if’s more effective than current treatments.

Immunotherapy is a powerful treatment, but doesn’t work for everyone and can have serious side effects. But a small, early study suggests combining information from different cancer scans could offer a way to predict if immunotherapy will work. Researchers used a computer programme to gauge the likelihood of treatment being successful, without the need for an invasive tissue sample (biopsy). Check out our news report for more.

And finally

The World Health Organisation (WHO) received a huge backlash to its appointment of Zimbabwe’s president Robert Mugabe as a goodwill ambassador. Many countries and health bodies criticised the decision citing a ‘long track record of human rights violations’, and a few days later the WHO’s head reversed the decision. The Guardian and Independent covered this story.

Michael



from Cancer Research UK – Science blog http://ift.tt/2zMqviM

This week we reported that MPs have launched an inquiry into e-cigarettes. The House of Commons Science and Technology Select Committee wants to find out what evidence is missing around e-cigs and their health effects. Public Health England estimates that e-cigarettes are far safer than tobacco, but other countries have taken different approaches. BBC News has more.

Cancer patients are less likely to have chemotherapy if diagnosed early, reports the Huffington Post. The new data report shows that patients whose cancer was diagnosed early were more likely to have surgery than chemo or radiotherapy. Our blog post has more.

We covered a small study that found the most aggressive type of ovarian cancer develops from cells that come from the fallopian tubes rather than the ovaries. Until recently it was thought that the disease developed from cells lining the surface of the ovary, but the new work could lead to new ways to prevent and treat it. The Independent also had this story.

Number of the week

65

New genetic variants found to increase the risk of breast cancer by a small amount

Junk food promotions in Scotland will be restricted under plans reported by BBC News. The Scottish government wants to limit deals on foods high in fat, sugar and salt, and could push for powers to ban TV adverts for unhealthy foods before the 9pm watershed. The Herald and iNews also had the story.

New DNA changes that increase the risk of breast cancer by a small amount have been identified, reports the Guardian. These 65 new variants, combined with the 180 already known, account for around a fifth of the increased risk that comes from inheriting the faulty genes. The Independent also covered this story.

Different types of brain tumours may share similar survival strategies, reports Medical Xpress. Surprisingly, a new study found the way cells from different kinds of brain tumour generate and use energy is similar, opening up new treatment research avenues. Check out our blog post for more.

An experimental gene therapy has shown promise for treating some brain tumour patients. We reported on a small clinical trial that found the therapy to be safe in patients with a kind of tumour called glioma, and the researchers will now see if’s more effective than current treatments.

Immunotherapy is a powerful treatment, but doesn’t work for everyone and can have serious side effects. But a small, early study suggests combining information from different cancer scans could offer a way to predict if immunotherapy will work. Researchers used a computer programme to gauge the likelihood of treatment being successful, without the need for an invasive tissue sample (biopsy). Check out our news report for more.

And finally

The World Health Organisation (WHO) received a huge backlash to its appointment of Zimbabwe’s president Robert Mugabe as a goodwill ambassador. Many countries and health bodies criticised the decision citing a ‘long track record of human rights violations’, and a few days later the WHO’s head reversed the decision. The Guardian and Independent covered this story.

Michael



from Cancer Research UK – Science blog http://ift.tt/2zMqviM
Aucun commentaire:
Libellés :

A potential human habitat on the moon?

The Marius Hills Skylight, as observed by the Japanese SELENE/Kaguya research team. Image via NASA/Goddard/Arizona State University.

A study published in Geophysical Research Letters on October 17, 2017 says that a hole in the moon’s Marius Hills – a region with a set of volcanic domes – is a skylight of a large open lava tube that could be used to protect astronauts from hazardous conditions on the surface. It could be large enough, the researchers say, to house an underground lunar city.

No one has ever been on the moon longer than three days, largely because space suits alone can’t shield astronauts from its elements: extreme temperature variation, radiation, and meteorite impacts. Unlike Earth, the moon has no atmosphere or magnetic field to protects its inhabitants.

The safest place to seek shelter is the inside of an intact lava tube, according to the study.

Lava tubes are naturally-occurring channels that form when a lava flow develops a hard crust, which thickens and forms a roof above the still-flowing lava stream. Once the lava stops flowing, the tunnel sometimes drains, forming a hollow void. Lava tubes exist on Earth, but the ones on the moon are much larger.

The city of Philadelphia is shown inside a theoretical lunar lava tube. Image via Purdue University/David Blair.

The Marius Hills hole was first discovered by the Japanese SELenological and ENgineering Explorer (SELENE), and has been the subject of much research and speculation. The new study, the scientists say, confirms that the opening is a skylight of a large underground lava tube.

Junichi Haruyama is a senior researcher at JAXA, Japan’s space agency. Haruyama said in a statement:

It’s important to know where and how big lunar lava tubes are if we’re ever going to construct a lunar base.

For the study, the researchers analyzed data from the SELENE spacecraft, and consulted scientists from the GRAIL mission, a NASA effort to collect high-quality data on the moon’s gravitational field.

Read more about how the researchers did the study.

The researchers say that, if the gravity results are correct, the lava tube near the Marius Hills is spacious enough to house one of the largest U.S. cities.

Bottom line: A large open lava tube in the moon’s Marius Hills region could protect astronauts from hazardous conditions on the lunar surface. It might someday be a good spot for a city on the moon.

Read more from Purdue University



from EarthSky http://ift.tt/2gGdG1K

The Marius Hills Skylight, as observed by the Japanese SELENE/Kaguya research team. Image via NASA/Goddard/Arizona State University.

A study published in Geophysical Research Letters on October 17, 2017 says that a hole in the moon’s Marius Hills – a region with a set of volcanic domes – is a skylight of a large open lava tube that could be used to protect astronauts from hazardous conditions on the surface. It could be large enough, the researchers say, to house an underground lunar city.

No one has ever been on the moon longer than three days, largely because space suits alone can’t shield astronauts from its elements: extreme temperature variation, radiation, and meteorite impacts. Unlike Earth, the moon has no atmosphere or magnetic field to protects its inhabitants.

The safest place to seek shelter is the inside of an intact lava tube, according to the study.

Lava tubes are naturally-occurring channels that form when a lava flow develops a hard crust, which thickens and forms a roof above the still-flowing lava stream. Once the lava stops flowing, the tunnel sometimes drains, forming a hollow void. Lava tubes exist on Earth, but the ones on the moon are much larger.

The city of Philadelphia is shown inside a theoretical lunar lava tube. Image via Purdue University/David Blair.

The Marius Hills hole was first discovered by the Japanese SELenological and ENgineering Explorer (SELENE), and has been the subject of much research and speculation. The new study, the scientists say, confirms that the opening is a skylight of a large underground lava tube.

Junichi Haruyama is a senior researcher at JAXA, Japan’s space agency. Haruyama said in a statement:

It’s important to know where and how big lunar lava tubes are if we’re ever going to construct a lunar base.

For the study, the researchers analyzed data from the SELENE spacecraft, and consulted scientists from the GRAIL mission, a NASA effort to collect high-quality data on the moon’s gravitational field.

Read more about how the researchers did the study.

The researchers say that, if the gravity results are correct, the lava tube near the Marius Hills is spacious enough to house one of the largest U.S. cities.

Bottom line: A large open lava tube in the moon’s Marius Hills region could protect astronauts from hazardous conditions on the lunar surface. It might someday be a good spot for a city on the moon.

Read more from Purdue University



from EarthSky http://ift.tt/2gGdG1K
Aucun commentaire:
Libellés :
Inscription à : Articles (Atom)