IPCC

I found the most inspiring statement from the Intergovernmental Panel on Climate Change (IPCC)'s 5th Assessment report, published on 1 October 2013 following its recent meeting in Copenhagen. The document came to the conclusion that ‘it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century’.

There you have it, as good as you will ever get from scientists (who have to wrap findings up in the language of statistical significance); a conclusion from 209 lead authors and 50 review editors from 39 countries and more than 600 contributing authors from 32 countries: climate change is a result of human activity. That leaves climate change doubters little room to manoeuvre.

And if there was any doubt left, the report concludes that:

‘Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased’. It does not matter that in the last 10 years temperature increases have stabilised; this is probably due to the redistribution of energy within the oceans and biosystems. In the Northern Hemisphere, 1983–2012 was the warmest 30-year period of the last 1400 years. The long-term trend is clear.

Almost the entire globe has experienced surface warming. Some of the evidence is startlingly clear. For example: ‘Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover has continued to decrease in extent.’ Over the period 1901–2010, global mean sea levels rose by 0.19 [0.17 to 0.21] m. Scientists allege that ‘CO2 concentrations have increased by 40% since pre-industrial times’.

What of the future? The headlines are not happy reading. Global surface temperatures are likely to rise by 1.5 – 2 °C by 2100. Heat will penetrate from the surface to the deep ocean and affect ocean circulation and many other aspects of the climate’s climatic patterns. Perhaps most significant is the prediction that temperatures will continue to rise for centuries to come, even if we stop carbon emissions right now.

One aspect also worth mentioning is that the effects of climate change will not affect everyone in the same way or to the same extent. For example, the contrast in precipitation between wet and dry regions and between wet and dry seasons will increase. This is likely to have a relatively harsher impact on fragile environments and render uninhabitable those areas where some of the least wealthy and least resilient communities live such as sub-Saharan Africa and parts of Asia. How will the world's communities react? The IPCC’s report is not designed to answer these sorts of questions, but in light of the evidence, the answers seem pretty self-explanatory.

David Jackman