Climate: "Positive Feedbacks Are Already Operating"
19 Nov, 2007 10:42 am
Scitizen interviews Dr. James Hansen, who heads the NASA Goddard Institute for Space Studies, for a look back at the events of 2007.
Dr Jim Hansen: No. They have only learned that there is an important issue, and that
humans are responsible for the situation, but the cacophony has not informed them well about what needs to be done.
S: What is your opinion with the conclusions and forecast of the IPCC group I report released earlier this year?
JH: The IPCC report is very useful, because it shows that even with the constraints that it operates under, the evidence that humans are responsible for global warming is so strong that it cannot be denied. That report requires sign-off by all countries including, for example, Saudi Arabia, so it is very cautious and conservative. This helps, in a way, because it creates an aura of being 'authoritative'.
S: The speed of the Arctic ice retreat shown by satellites has astonished scientists; as well, the year 2007 saw the melting record in Greenland for areas above 2000 meters. What should we learn from these situations?
JH: These are illustrations of physical mechanisms that contribute to climate tipping points, A tipping point occurs when climate change reaches a point such that, because of warming already 'in the pipeline' and positive climate feedbacks, very little if any additional climate forcing is needed to cause rather rapid, large climate impacts. One reason that these changes in the Arctic are beginning to accelerate is that the melting of sea ice exposes dark ocean water, and meltwater on the surface of Greenland makes the snow surface darker. These changes cause the ocean and ice sheet to absorb more sunlight and accelerate melting.
S: Do you agree with the concept of "tipping point", the point at which a positive feedback loop beings? Are we about to reach such a point?
JH: We have already reached a point at which these positive feedbacks are operating. They are not run-away feedbacks, however, i.e., feedbacks that can by themselves now proceed to cause very large planetary changes. They still require human-made forcings. If we reduce these forcings we can still stop the climate change. The forcings include, in addition to carbon dioxide, methane, low-level ozone, and black soot. A program focused on all of these could stop the climate change, even though some further increase of carbon dioxide is inevitable given the infrastructure that is in place.
S: A recent study published in the PNAS suggests that Earth's atmosphere is accumulating carbon dioxide faster than current predictions. What is your opion on current public policiees, such as the Kyoto Protocol, which proposes to set a limit on CO2 emissions?
JH: That study was misleading. The usual definition of the 'airborne fraction' of carbon dioxide is the ratio of the observed increase in atmospheric CO2 divided by the emissions of CO2 into the air from fossil fuel burning. That is the best definition, because those are
the two numbers that we know accurately. With that definition we see that the airborne fraction of CO2 is about 57% of the emissions. That percentage fluctuates from year to year, but it has not been increasing. The atmosphere has not been accumulating CO2 faster than expected, rather it is just as fast as expected, but the world is still (foolishly) increasing the rate of CO2 emissions. The PNAS story confused the public by using a definition of airborne fraction that included such terms as CO2 released from cutting down trees, growing trees, bad soil practices, good soil practices, etc., but we just do not know those terms accurately, so they can report any answer-- it is useful research to try to estimate those terms, but they manage to confuse the public.
S: Also, the "after-Kyoto" is now being discussed. What measures do you think should be taken?
JH: The climate problem is solvable via actions that make sense for other reasons and which will have many ancillary benefits, including cleaner air and water, improved public health, increased agricultural productivty, and preservation of the environment and species.
The two primary actions required are a moratorium on new coal-fired power plants (until technology for carbon capture is ready) and a gradually increasing price on carbon emissions. The latter can be done in a way such that the small user, by making choices to save more emissions than the average, can actually gain financially. Government leadership is needed to make these two actions work, e.g., rules for utilities must be changed such that they make more profit when they help improve energy efficiency -- now they make more money if they sell us more energy.
In addition to these two primary actions, we need some focused programs to reduce the non-CO2 climate forcings, especially methane emissions and black soot.
A clearer discussion of these matters is available in my testimony "Iowa Coal Case", available here.