IPPC 5th Assessment Report

On the 30^th September the Intergovernmental Panel on Climate Change (IPCC) launched the first part of their 5^th Assessment report, the 4^th having been published in 2007, which analyses and synthesises the latest data, projections and physical evidence for climate change. The dominant message from the report from working group I of the IPCC is that scientists are surer than ever that climate change is due to human related activities.

The contributions of working groups II and III, and the overall synthesis report are to be published sequentially ending in October 2014.

The IPCC, which provides “a clear scientific view on the current state of knowledge in climate change and its potential environmental and socio-economic impacts”, has convened over 800 climate scientists from around the world to produce a landmark report on the state of climate change in the world. We summarise some of the key findings here:

• It is extremely likely that human influence has been the dominant cause of global warming since the mid-20^th century. Over half of the increase in global surface temperatures between 1951 and 2010 can be attributed to human activities.
• The period from 1983-2012 in the Northern Hemisphere was probably the warmest 30-year period of the last 1,400 years.
• Projections of the highest emissions scenario show an increase in the global average temperature of 4°C by 2100. With significant emissions reductions, the report explains, global temperature increase can be limited to below 2°C but with a doubling of CO₂ in the atmosphere, we are likely to see an average change in temperature of between 1.5°C and 4.5°C. Warming above 2°C is considered a critical threshold above which we can expect “dangerous” impacts.
• The report warns of the long lasting effects of greenhouse gas emissions, which will remain in the atmosphere and warm the climate for centuries to come even with immediate and significant mitigation activities. Some 15% to 40% of released CO₂ will remain in the atmosphere longer than 1,000 years after those emissions have ended.
• Sea levels are expected to rise faster than in the last 40 years. In this century, sea levels are projected to rise between 26cm and 82cm, dependent on greenhouse emissions.
• The Gulf Stream (or Atlantic Ocean circulation) is expected to weaken by 12% to 54% by the end of the century.
• Over the last two decades, the Greenland and Antarctic ice sheets have been shrinking. The report states that if emissions continue unabated the Arctic Ocean will likely become virtually ice-free in summer before the middle of the century.
• It is “virtually certain” that sea level rise will continue beyond 2100 and sustained warming above some unknown threshold will lead to the melting of the Greenland Ice Sheet, which would cause a global mean sea level rise of up to 7m. The total loss of the Greenland ice sheet is estimated to occur at 1 to 4°C of warming above preindustrial temperature.
• The atmospheric concentration of carbon dioxide (CO₂) has increased by 40% since pre-industrial times. Average increases in CO₂, methane (CH₄) and nitrous oxide (NO₂) are believed, with high confidence, to be far higher than increases occurring in the last 22,000 years.
• The recent slowing down of temperature increases, seen in the last 15 years, is not considered a long enough timescale to come to any conclusions.

Although these findings are worrying enough, to achieve this consensus around the physical impacts of climate change, the estimates can be considered conservative.

For many, who have already accepted human-induced climate change, there is a less of a question of what is physically happening and more of a concern over what we are going to do about it. We will have to wait for the next instalments of the IPCC 5^th report and hope that their impact is significant enough to motivate the world to act.

Where are we on climate change?

Professor Sir Brian Hoskins, Director of the Grantham Institute for Climate Change and advisor to the UK government through the Committee on Climate Change, recently gave a talk at Imperial College London on the latest research and actions around climate change.

Global CO₂ levels are currently at 397ppm (parts per million), a level not seen for 4.5 million years. We have increased CO₂ levels in the atmosphere by 40% since the Industrial Revolution. While there has been a clear and significant increase in global temperatures since 1850, we have seen a hiatus on temperature rises in the last decade. While sceptics may use this as evidence to support their claims, a decade of cooler temperatures is not outside the range of predictions from climate models.

Global sea levels are rising 3mm per year. While the melting of the Western Antarctic and Greenland ice sheets is contributing around 1mm of this increase, it is unknown how likely this is to accelerate if we reach a threshold point of destabilisation. In the Arctic, recent pictures of the ice cap in mid-September (when it is at its minimum size) show it is half the average size it was in the last century. By 2050-2060 we would expect the arctic ice cap to have vanished come September.

We have seen some significant heat extremes in the past decade: the 2003 European heatwave, 2010 Russian heatwave and more recently the 2012 US drought. Work by NASA scientists Dr James Hansen and colleagues indicates a shift to more frequent and severe bouts of high temperatures. But it is not just heat extremes, as the climate changes we are also seeing cold extremes in certain locations despite remarkable warmth elsewhere. This indicates our ability to predict regional trends is much more limited than our ability to predict global averages and while we may, in the past have viewed climate change as a warming of the planet, now we are trying to understand it as a disruption of our climate systems, one that will have severe and varied results.