John Lanchbery Principal Climate Change Advisor
Finally, we have it - after all the waiting and tit-for-tat teases from the various interests, the Intergovernmental panel on Climate Change (IPCC) has published the summary of its report on climate science. And it’s pretty strong stuff.
The two page headline findings are as clear and concise as you are going to get for a complicated subject. Quite an achievement after a week of conference, science, questions and ultimate agreement that ended in the small hours of this morning (Friday). How they get these out on time is remarkable in itself. There’s more detail in the full summary report and next week, the full 2,000 page report will be available.
Even more clear, what US Secretary of State, John Kerry, said about the IPCC report this morning, “Climate change is real, it’s happening now, human beings are the cause of this transformation, and only action by human beings can save the world from its worst impacts ... If this isn’t an alarm bell, then I don’t know what one is.”
So what does it actually say? First, it is more certain than ever (95% sure) that climate change is due mainly to human activities. Since 1880, the average surface temperature of the Earth has risen by 0.85OC, more over the land than the sea and more at high latitudes. The air temperature rise over land north of 65oN is, for example, between 2.5 and 3 degrees. Each of the three most recent decades has been warmer than all previous decades, since 1850 – the last decade has seen a slowdown in the rate of increase, not a halting or even a reversal in global temperature increase, as some may have had you believe.
As a consequence, sea level rise has accelerated, rising nearly twice as fast in the last two decades than previously. Melting of both glaciers and ice sheets has, overall, been several times faster in the last decade than in the 1990s. The extent of Arctic sea ice in summer (the seasonal minimum is in September) has decreased markedly in recent years. The area covered by Arctic sea ice has shrunk in every decade since 1979. There is strong evidence that temperature extremes, such as warm days and heat waves, have become more common since the 1950s. The oceans are acidifying (by 26% so far) due to the rise in atmospheric concentrations of carbon dioxide. All of these changes are expected to increase, some at an increasing rate.
On our current emission pathways, average global temperatures will rise well beyond the universally agreed safe limit of two degrees by the end of the century. The IPCC gives a global carbon budget consistent with staying below two degrees. To have a good chance (greater than 66%) of doing so, cumulative carbon dioxide emissions need to be 800 Gtonnes. We’ve already used 541 Gt of this by 2011, so we’re well over halfway through our budget.
Not a great outlook, but neither should we despair. As Martin Harper says in his blog, together we can avoid dangerous climate change. We can, and we should – no, we must: we owe that to all the life, ours included, that makes the beauty and our home on this place we call Earth.