23rd May, 2010 - Posted by admin - Comments Off
The need for a Plan B for Climate Change
Plan A is the UK Government’s current plan for addressing climate change. It relies on reducing the emissions of long lived greenhouse gases, especially carbon dioxide, during this century. It emphasises keeping the level long lived greenhouse gasses below a peak level at which dangerous climate change becomes probable.
The view of some respected scientists is that Plan A does not address the risk of triggering dangerous climate change sooner than expected. Plan B is delays global temperature rises by means that have an immediate effect. It places emphasis on the reduction of short term climate forcing agents such as methane and black carbon. It also advocates geoengineering schemes to
- reduce the amount of sunlight reaching the Earth’s surface
- extract carbon dioxide from the atmosphere.
Plan B and climate feedbacks
Professor Peter Cox, a leading climate scientist, says:
There should be a plan B for climate change if reducing emissions of CO2 cannot be effected soon enough. This would take more seriously the effects of pathways with shorter timescales than CO2, such as methane, ozone (NOx as a precursor) and black carbon. Plan B should also consider geoengineering: Sulphate [released into the upper atmosphere] looks best.
There is another reason for a Plan B - underestimated or unacknowledged climate feedbacks. Feedbacks occur when increasing temperature trigger mechanisms, which further contribute to global warming. One example is the release of methane from the Arctic tundra and Arctic seas. This is important because methane is a powerful greenhouse gas and there are very large quantities stored in the Arctic. There have been recent reports of increased methane emissions in the Arctic. See Science, “Extensive Methane Venting to the Atmosphere from Sediments of the East Siberian Arctic Shelf” by Shakhova et.al. (http://www.sciencemag.org/cgi/content/short/327/5970/1246)
Another feedback happens when melting Arctic sea ice leaves areas of open sea. Professor Peter Wadhams, who has been studying the Arctic ice since the 1960s says:
The case of Arctic ice is somewhat of a tipping point since the open water created during summer warms up, to about 5C at present, and this slows down the subsequent autumn freeze up, giving less winter growth. The area of multi-year ice is also shrinking to the point where almost the whole ice cover will be susceptible to summer melt. It may grow back a little in a cold winter but in my view it can never get back to its original situation of, say, 40 years ago. In this sense it has passed through a tipping point.
Plan B is needed because the UK Government’s current plan, Plan A, does not cope with these contingencies:
- A failure to control global greenhouse emissions soon
- Feedbacks reacting more strongly than expected.
The UK Government’s Plan
Government thinking is that the total amount of carbon dioxide emitted is important – not precisely when the emissions occur. This view is clearly influenced by Allen et al, “Warming caused by cumulative carbon emissions towards the trillionth tonne”. They say
Total anthropogenic emissions of one trillion tonnes of carbon (3.67 trillion tonnes of CO2), about half of which has already been emitted since industrialization began, results in a most likely peak carbon-dioxide induced warming of 2 degrees Celsius above pre-industrial temperatures, with a 5–95% confidence interval of 1.3–3.9 degrees Celsius.
It is apparent that certain climate feedbacks have not been incorporated into the computer simulations used by Allen et. al. but this paper has installed the peak level of carbon dioxide as the keystone in current government thinking.
The Committee on Climate Change
In “Building a low-carbon economy” (December 2008), the Committee on Climate Change say:
The UK should strongly support a global commitment to cutting GHG emissions by at least 50% below current levels by 2050, with total global Kyoto GHG emissions between 20-24 billion tonnes CO2e in 2050, and with further reductions to between 8-10 billion tonnes CO2e required by 2100. Cuts of this scale would limit our central expectation of temperature rise by 2100 to as close to 2°C as possible, and reduce the risk of extremely dangerous climate change to very low levels (e.g. less than a 1% chance of 4°C temperature rise). CO2e concentrations would peak at around 500ppm by the end of the century before falling towards 450ppm.
This emphasis on long-lived greenhouse gases is consistent with Allen et. al. The attitude to short-lived species, such as methane, can be summarized as
By the time peak temperature occurs any methane (or other short-lived species) released now will have been removed from the atmosphere by natural processes so will not affect global warming at the all-important peak.
Plan A and Plan B compared
Plan A aims at keeping levels of long-lived greenhouse gases below an “safe” maximum level in order to limit the rise in global temperatures to below 2 degrees Celsius – regarded as a limit beyond which dangerous climate change can occur. It is a long-term plan, the maximum concentration occurring towards the end of the century. Plan B limits temperature rises over a shorter time span. It places more emphasis on the reduction of short lived climate forcing agents (e.g. methane and soot) to reduce the risk of feedbacks. It also extracts carbon dioxide from the atmosphere.
Plan A runs the risk of
- triggering unexpected climate feedbacks as temperature rises
- larger than expected global greenhouse gas emissions
Plan B delays global warming, allowing more time to cut the emissions of long-lived greenhouse gases and engineer them from the atmosphere. V. Ramanathan from the Scripps Institution of Oceanography recently gave a testimonial to the House Select Committee on Energy Independence and Global Warming. His testimonial gives support to this idea:
At current rate of emission (35 billion tons per year) and the current growth rate of 2% to 3%, the manmade greenhouse effect can double during this century. BC reductions [Black Carbon reductions], even at 50%, cannot offset the CO2 effect. However, BC reductions when combined with reductions in other short lived climate warming gases, can delay large warming by few decades and complement CO2 mitigation efforts.
Plan B also extracts carbon dioxide from the atmosphere so does not rely solely on cutting emissions. We need Plan B because Plan A may be already failing.