A report by the UK-based Global Warming Policy Foundation claims that the United Nations has hidden lower estimates of the future extent of global warming.
Estimates of how much global warming will happen over the next 70-100 years if carbon dioxide levels doubled have been reduced. The measure, known as “climate sensitivity”, is a range of likely temperature increase over some period of time.
The United Nations Intergovernmental Panel on Climate Change (IPCC) reports a range of project warming that does not accurately reflect how climate sensitivity has been adjusted downward, according the Foundation’s report.
A 2007 report from the IPCC reported that the global average temperature would increase by 3 degrees Celsius by the end of the century. This figure was taken from a calculated range of 2 to 4.5 degrees. Later temperature measurements showed little warming, so the low-end of the temperature range was revised to 2 degrees in a century, then 1.5 degrees over 70 years.
The 2013 IPCC assessment reports a range of 1.5 to 4.5 degrees over the next 100 years, without giving a point estimate as did earlier reports. The reason for this change is not given in the original report, but is briefly addressed in a summary published in January of 2014.
In addition to the wider climate sensitivity estimate, there is disagreement between estimates based on global temperature data and estimates from climate change models. According to a study by Nik Lewis, a UK climate scientist, and Dutch science writer Marcel Crok estimates of mean temperature between 2081 and 2100 are 40-80% less when estimating from temperature data.
Policy makers use climate sensitivity to predict likely temperature changes, and the associated economic costs. The policy decisions based on climate sensitivity can have vast, and potentially expensive, consequences. The Obama administration used climate sensitivity number to create a social cost of carbon (SCC) number that reflects the cost of each ton of carbon dioxide pollution.
The old SCC estimate of $21 per ton was raised to $37 per ton, before President Obama made public a plan to cut carbon dioxide emissions in the United States by 17% by 2020. The higher SCC increases the estimated cost of carbon dioxide pollution and makes climate change policies look less expensive. Each ton of carbon dioxide not emitted results in greater benefits to society, so a greater investment can be justified.
The Foundation’s report seems to cast doubt on the usefulness of that increase in the SCC. If climate sensitivity is less than used in that SCC calculation, then the increase will impose unnecessary costs on society. The lack of a central estimate from the IPCC makes the Obama administration’s calculation questionable. According to the Foundation, this uncertainty about the numbers means that no SCC should be published until the UN can supply a reliable central estimate of temperature changes.
The Global Warming Policy Foundation is a UK-based think tank and educational charity dedicated to “restoring balance and trust to the climate debate” according to their Web site. Their work is intended to address the likely effects of global warming and the implications of policy response to climate change.
By Chester Davis