Subscribe
Home > Blogs & Communities > Findings > Climate Change Worst-Case Scenarios: Not Worst Enough  

Fill 'Er Up With Rainforest | Main | Sponging Away Antibiotic Resistance

February 14, 2009

Climate Change Worst-Case Scenarios: Not Worst Enough

Grinnell Glacier, MontanaThe news on climate change seemed bad enough in 2007, when the Intergovernmental Panel on Climate Change (IPCC) announced in their fourth assessment report that "warming of the climate system is unequivocal," that humans were "very likely" to blame, and that if we keep pumping greenhouse gases into the atmosphere, climate will "very likely" change much more than it did in the 20th century. But researchers reported today that, in the 2 years since the report was released, the news has gotten even worse.

Climate scientist Chris Field of Stanford University relayed the first bit of bad news to a sober audience during his talk, "What is New and Surprising since the IPCC Fourth Assessment." According to a paper his group published in the Proceedings of the National Academy of Sciences in 2007, humans are now pumping out climate-warming gases nearly three times faster than the IPCC authors anticipated in their worst-case scenario. Specifically, Field described how carbon emissions had been increasing at 0.9% per year through the 1990s, but accelerated to 3.5% per year growth between 2000 and 2007.

Why the disparity?

The acceleration, it turned out, was mostly due to economic growth in quickly developing economies, particularly China, and the move toward burning coal, which produces more CO2 per unit of energy than any other fossil fuel. But before Americans feel too smug, he reminded the U.S. that it still emits far more CO2 per capita than China.

Sea-level rise is also looking more ominous. Climate researcher Anny Cazenave of the Centre National d'Etudes Spatiales in Toulouse, France, followed Field's presentation with news that sea level is now rising twice as fast as it had been for the last half-century. In 2007, the IPCC had reported that sea level had been rising 1.7 mm per year since the 1960s. Cazenave described precise measurements of sea level from orbiting satellites that show average sea levels rising 3.35 millimeters per year from 1993 through 2008.

The odd thing is that sea level is not rising for the same reasons it was just a few years ago. Sea level rises because warming ocean water expands, and it rises because more water from glaciers and ice sheets melt into the sea. For reasons that Cazenave says are not understood, water stopped expanding, perhaps temporarily, a few years ago. But sea level kept rising, which means that the water had to come from land. Sure enough, by cross-checking measurements of ice lost from ice sheets and glaciers, the researchers showed that whereas melting land ice accounted for just 40% of sea level rise between 1993 and 2003, it now accounts for 80%.

In a comment that could sum up the whole session, Field said, "I don't think there's anything here that should be taken as reassuring."

--Dan Ferber

2 Comments

Well, here’s something reassuring. The thermal expansion of seawater at 15°C (average temperature of earth surface air) is .15% per degree C.

If we take the turnover time of the world’s oceans as 300 years (Munk’s figure of vertical diffusivity would suggest 150 years by the way), then since 1900 roughly a third of the oceans’ seawater has been in contact with surface air.

The average depth of the oceans is 4000m, so 1500m has been in contact with surface air since 1900

So the average temperature rise in this seawater is:

1.5mm per year (due to thermal expansion) / 1,500,000 mm / .0015

which gives 0.0007 degrees C per year, or 0.07 degrees C since 1900.

which suggests the famous hockey stick (0.4 degrees C rise in global surface temperatures since 1900) is exaggerated by a factor of about 5

Good news!

C.Field mentions the potential of a drying out Amazon burning up in forest fires.

If the Amazon does dry out and become susceptible to large conflagerations, I suggest logging channels through the dry areas pre-emptively (years in advance) as a firebreak. This forestry mangement practise would treat the Amazon as a checkerboard, and the logged strips would be the "lines" separating the checker squares, with the remaining rainforest separated into unconnected "squares".
If AGW-dried rainforests are tinder boxes, cutting up the Amazon would keep forest fires isolated, keep the carbon out of the air. The cuts would have to be large enough to prevents winds and convection currents beyond the firebreak to an adjacent non-cindered forest; visible from space and probably tens of km wide. This practise would shatter biomes and ecosystems of the largest incabator of new species on Earth. Some of the species could be reintroduced if the Amazon were ever healed one day.
A much more ambitious geoengineering approach would utilize irrigation and massive river diversions to effect the same firebreak. Except instead of logging, the idea would be to keep the drying out rainforest "wet" enough throughout designated "checkerboard line" areas that are identical to the logged areas in function as a forest fire barrier.