Simple science sound bites

At the end of last week the UN's IPCC fifth assessment report on climate change started to see the light of day with the publication of the Summary for policy makers. During an idle hour or two I decided to try and read it. I'm afraid I struggled with some of the science. One issue that strikes you, however, is that even the scientists have struggled to get across the concepts of levels of certainty and uncertainty. I guess events around the War in Iraq and then the debates around the Syrian crisis have shown us all that we need to better understand the basis on which claims are made.

This means that each statement is accompanied by caveats around the degree of certainty. Here are some examples.

1. "Warming of the climate system is unequivocal". This is about the most definitive statement in the whole report.

2. "Each of the last three decades has been successively warmer at the Earth's surface than any preceding decade since 1850". This statement has 'medium confidence" attached to it.

3. A bit later the report states, this time with high confidence that "Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost world wide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent". 

The report then goes on to look at some of the 'whys'. It says "human influence on the climate system is clear" and that "human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes". This seems a pretty long charge sheet and the IPCC say that the evidence has increased since their last report. The key sentence is therefore "IT IS EXTREMELY LIKELY THAT HUMAN INFLUENCE HAS BEEN THE DOMINANT CAUSE OF THE OBSERVED WARMING SINCE THE MID 20th CENTURY". I understand that in the last report a few years ago it was just 'highly likely' so extremely is an attempt to show an increase in confidence.

That seems pretty clear to me. The report then tackles forecasts and as with any forecast the range of uncertainty is obviously much greater than that around explaining past behaviour. I decided to focus on the global mean temperature forecasts, over the last 120 years or so it has gone up around 0.6 degrees. The report details four scenarios for the next 60 years and they all have ranges of temperature increases as follows:

Scenario 2.6.    0.4 to 1.6

Scenario 4.5.    0.9 to 2.0

Scenario 6.0.    0.8 to 1.8 

Scenario 8.5.    1.4 to 2.6

By my reckoning even the lowest estimate of the lowest range shows warming quicker than we have experienced in modern times  (my maths says about about 30% quicker) and a sort of completely unscientific range in the middle of the four scenarios would suggest it could be around three to four times faster. Given the changes in the various ecosystems we have already seen that ranges from the extremely worrying to the postively frightening. 

And finally one more quote which neatly summarises what has to be done. "Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions. ". My sentiments entirely although I would add one more S. Soon.