Yes, a few climate models give unexpected predictions – but the technology remains a powerful tool


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Nerilie Abram, Australian National University; Andrew King, The University of Melbourne; Andy Pitman, UNSW; Christian Jakob, Monash University; Julie Arblaster, Monash University; Lisa Alexander, UNSW; Sarah Perkins-Kirkpatrick, UNSW; Shayne McGregor, Monash University, and Steven Sherwood, UNSW

The much-awaited new report from the Intergovernmental Panel on Climate Change (IPCC) is due later today. Ahead of the release, debate has erupted about the computer models at the very heart of global climate projections.

Climate models are one of many tools scientists use to understand how the climate changed in the past and what it will do in future.

A recent article in the eminent US magazine Science questioned how the IPCC will deal with some climate models which “run hot”. Some models, it said, have projected global warming rates “that most scientists, including the model makers themselves, believe are implausibly fast”.


Read more: Monday’s IPCC report is a really big deal for climate change. So what is it? And why should we trust it?


Some commentators, including in Australia, interpreted the article as proof climate modelling had failed.

So should we be using climate models? We are climate scientists from Australia’s Centre of Excellence for Climate Extremes, and we believe the answer is a firm yes.

Our research uses and improves climate models so we can help Australia cope with extreme events, now and in future. We know when climate models are running hot or cold. And identifying an error in some climate models doesn’t mean the science has failed – in fact, it means our understanding of the climate system has advanced.

So lets look at what you should know about climate models ahead of the IPCC findings.

What are climate models?

Climate models comprise millions of lines of computer code representing the physics and chemistry of the processes that make up our climate system. The models run on powerful supercomputers and have simulated and predicted global warming with remarkable accuracy.

They unequivocally show that warming of the planet since the Industrial Revolution is due to human-caused emissions of greenhouse gases. This confirms our understanding of the greenhouse effect, known since the 1850s.

Models also show the intensity of many recent extreme weather events around the world would be essentially impossible without this human influence.

 

 

 

Scientists do not use climate models in isolation, or without considering their limitations.

For a few years now, scientists have known some new-generation climate models probably overestimate global warming, and others underestimate it.

This realisation is based on our understanding of Earth’s climate sensitivity – how much the climate will warm when carbon dioxide (CO₂) levels in the atmosphere double.

Before industrial times, CO₂ levels in the atmosphere were 280 parts per million. So a doubling of CO₂ will occur at 560 parts per million. (For context, we’re currently at around 415 parts per million).

The latest scientific evidence, using observed warming, paleoclimate data and our physical understanding of the climate system, suggests global average temperatures will very likely increase by between 2.2℃ and 4.9℃ if CO₂ levels double.

The large majority of climate models run within this climate sensitivity range. But some don’t – instead suggesting a temperature rise as low as 1.8℃ or high as 5.6℃.

It’s thought the biases in some models stem from the representations of clouds and their interactions with aerosol particles. Researchers are beginning to understand these biases, building our understanding of the climate system and how to further improve models in future.

With all this in mind, scientists use climate models cautiously, giving more weight to projections from climate models that are consistent with other scientific evidence.

The following graph shows how most models are within the expected climate sensitivity range – and having some running a bit hot or cold doesn’t change the overall picture of future warming. And when we compare model results with the warming we’ve already observed over Australia, there’s no indication the models are over-cooking things.

Rapid warming in Australia under a very high greenhouse gas emission future (red) compared with climate change stabilisation in a low emission future (blue). Author provided.

What does the future look like?

Future climate projections are produced by giving models different possibilities for greenhouse gas concentrations in our atmosphere.

The latest IPCC models use a set of possibilities called “Shared Socioeconomic Pathways” (SSPs). These pathways match expected population growth, and where and how people will live, with plausible levels of atmospheric greenhouse gases that would result from these socioeconomic choices.

The pathways range from low-emission scenarios that also require considerable atmospheric CO₂ removal – giving the world a reasonable chance of meeting the Paris Agreement targets – to high-emission scenarios where temperature goals are far exceeded.


Nerilie Abram, based on Riahi et al. 2017, CC BY-ND

Ahead of the IPCC report, some say the high-emission scenarios are too pessimistic. But likewise, it could be argued the lack of climate action over the past decade, and absence of technology to remove large volumes of CO₂ from the atmosphere, means low-emission scenarios are too optimistic.

If countries meet their existing emissions reduction commitments under the Paris Agreement, we can expect to land somewhere in the middle of the scenarios. But the future depends on our choices, and we shouldn’t dismiss any pathway as implausible.

There is considerable value in knowing both the future risks to avoid, and what’s possible under ambitious climate action.


Read more: The climate won’t warm as much as we feared – but it will warm more than we hoped


Wind turbines in field
The future climate depends on our choices today. Unsplash

Where to from here?

We can expect the IPCC report to be deeply worrying. And unfortunately, 30 years of IPCC history tells us the findings are more likely to be too conservative than too alarmist.

An enormous global effort – both scientifically and in computing resources – is needed to ensure climate models can provide even better information.

Climate models are already phenomenal tools at large scales. But increasingly, we’ll need them to produce fine-scale projections to help answer questions such as: where to plant forests to mitigate carbon? Where to build flood defences? Where might crops best be grown? Where would renewable energy resources be best located?

Climate models will continue to be an important tool for the IPCC, policymakers and society as we attempt to manage the unavoidable risks ahead.The Conversation

Nerilie Abram, Chief Investigator for the ARC Centre of Excellence for Climate Extremes; Deputy Director for the Australian Centre for Excellence in Antarctic Science, Australian National University; Andrew King, ARC DECRA fellow, The University of Melbourne; Andy Pitman, Director of the ARC Centre of Excellence for Climate Extremes, UNSW; Christian Jakob, Professor in Atmospheric Science, Monash University; Julie Arblaster, Chief Investigator, ARC Centre of Excellence for Climate Extremes; Chief Investigator, ARC Securing Antarctica’s Environmental Future; Professor, Monash University; Lisa Alexander, Chief Investigator ARC Centre of Excellence for Climate Extremes and Professor Climate Change Research Centre, UNSW; Sarah Perkins-Kirkpatrick, ARC Future Fellow, UNSW; Shayne McGregor, Associate professor, Monash University, and Steven Sherwood, Professor of Atmospheric Sciences, Climate Change Research Centre, UNSW

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Fossil fuel emissions hit record high after unexpected growth: Global Carbon Budget 2017


Pep Canadell, CSIRO; Corinne Le Quéré, University of East Anglia; Glen Peters, Center for International Climate and Environment Research – Oslo; Robbie Andrew, Center for International Climate and Environment Research – Oslo; Rob Jackson, Stanford University, and Vanessa Haverd, CSIRO

Global greenhouse emissions from fossil fuels and industry are on track to grow by 2% in 2017, reaching a new record high of 37 billion tonnes of carbon dioxide, according to the 2017 Global Carbon Budget, released today.

The rise follows a remarkable three-year period during which global CO₂ emissions barely grew, despite strong global economic growth.

But this year’s figures suggest that the keenly anticipated global peak in emissions – after which greenhouse emissions would ultimately begin to decline – has yet to arrive.


Read more: Fossil fuel emissions have stalled: Global Carbon Budget 2016


The Global Carbon Budget, now in its 12th year, brings together scientists and climate data from around the world to develop the most complete picture available of global greenhouse gas emissions.

In a series of three papers, the Global Carbon Project’s 2017 report card assesses changes in Earth’s sources and sinks of CO₂, both natural and human-induced. All excess CO₂ remaining in the atmosphere leads to global warming.

We believe society is unlikely to return to the high emissions growth rates of recent decades, given continued improvements in energy efficiency and rapid growth in low-carbon energies. Nevertheless, our results are a reminder that there is no room for complacency if we are to meet the goals of the Paris Agreement, which calls for temperatures to be stabilised at “well below 2℃ above pre-industrial levels”. This requires net zero global emissions soon after 2050.

After a brief plateau, 2017’s emissions are forecast to hit a new high.
Global Carbon Project, Author provided

National trends

The most significant factor in the resumption of global emissions growth is the projected 3.5% increase in China’s emissions. This is the result of higher energy demand, particularly from the industrial sector, along with a decline in hydro power use because of below-average rainfall. China’s coal consumption grew by 3%, while oil (5%) and gas (12%) continued rising. The 2017 growth may result from economic stimulus from the Chinese government, and may not continue in the years ahead.

The United States and Europe, the second and third top emitters, continued their decade-long decline in emissions, but at a reduced pace in 2017.

For the US, the slowdown comes from a decline in the use of natural gas because of higher prices, with the loss of its market share taken by renewables and to a lesser extent coal. Importantly, 2017 will be the first time in five years that US coal consumption is projected to rise slightly (by about 0.5%).

The EU has now had three years (including 2017) with little or no decline in emissions, as declines in coal consumption have been offset by growth in oil and gas.

Unexpectedly, India’s CO₂ emissions will grow only about 2% this year, compared with an average 6% per year over the past decade. This reduced growth rate is likely to be short-lived, as it was linked to reduced exports, lower consumer demand, and a temporary fall in currency circulation attributable to demonetisation late in 2016.

Trends for the biggest emitters, and everyone else.
Global Carbon Project, Author provided

Yet despite this year’s uptick, economies are now decarbonising with a momentum that was difficult to imagine just a decade ago. There are now 22 countries, for example, for which CO₂ emissions have declined over the past decade while their economies have continued to grow.

Concerns have been raised in the past about countries simply moving their emissions outside their borders. But since 2007, the total emissions outsourced by countries with emissions targets under the Kyoto Protocol (that is, developed countries, including the US) has declined.

This suggests that the downward trends in emissions of the past decade are driven by real changes to economies and energy systems, and not just to offshoring emissions.

Other countries, such as Russia, Mexico, Japan, and Australia have shown more recent signs of slowdowns, flat growth, and somewhat volatile emissions trajectories as they pursue a range of different climate and energy policies in recent years.

Still, the pressure is on. In 101 countries, representing 50% of global CO₂ emissions, emissions increased as economies grew. Many of these countries will be pursuing economic development for years to come.

Contrasting fortunes among some of the world’s biggest economies.
Nigel Hawtin/Future Earth Media Lab/Global Carbon Project, Author provided

A peek into the future

During the three-year emissions “plateau” – and specifically in 2015-16 – the accumulation of CO₂ in the atmosphere grew at a record high that had not previously been observed in the half-century for which measurements exist.

It is well known that during El Niño years such as 2015-16, when global temperatures are higher, the capacity of terrestrial ecosystems to take up CO₂ (the “land sink”) diminishes, and atmospheric CO₂ growth increases as a result.

The El Niño boosted temperatures by roughly a further 0.2℃. Combined with record high levels of fossil fuel emissions, the atmospheric CO₂ concentration grew at a record rate of nearly 3 parts per million per year.

This event illustrates the sensitivity of natural systems to global warming. Although a hot El Niño might not be the same as a sustained warmer climate, it nevertheless serves as a warning of the global warming in store, and underscores the importance of continuing to monitor changes in the Earth system.

The effect of the strong 2015-16 El Niño on the growth of atmospheric CO₂ can clearly be seen.
Nigel Hawtin/Future Earth Media Lab/Global Carbon Project, based on Peters et al., Nature Climate Change 2017, Author provided

No room for complacency

There is no doubt that progress has been made in decoupling economic activity from CO₂ emissions. A number of central and northern European countries and the US have shown how it is indeed possible to grow an economy while reducing emissions.

Other positive signs from our analysis include the 14% per year growth of global renewable energy (largely solar and wind) – albeit from a low base – and the fact that global coal consumption is still below its 2014 peak.


Read more: World greenhouse gas levels made unprecedented leap in 2016


These trends, and the resolute commitment of many countries to make the Paris Agreement a success, suggest that CO₂ emissions may not return to the high-growth rates experienced in the 2000s. However, an actual decline in global emissions might still be beyond our immediate reach, especially given projections for stronger economic growth in 2018.

The ConversationTo stabilise our climate at well below 2℃ of global warming, the elusive peak in global emissions needs to be reached as soon as possible, before quickly setting into motion the great decline in emissions needed to reach zero net emissions by around 2050.

Pep Canadell, CSIRO Scientist, and Executive Director of the Global Carbon Project, CSIRO; Corinne Le Quéré, Professor, Tyndall Centre for Climate Change Research, University of East Anglia; Glen Peters, Research Director, Center for International Climate and Environment Research – Oslo; Robbie Andrew, Senior Researcher, Center for International Climate and Environment Research – Oslo; Rob Jackson, Chair, Department of Earth System Science, and Chair of the Global Carbon Project, globalcarbonproject.org, Stanford University, and Vanessa Haverd, Senior research scientist, CSIRO

This article was originally published on The Conversation. Read the original article.