Clear and Present Danger: A Conversation With Nobel Laureate Steve Chu on the Risks of Climate Change

Why We Should Be Scared

If the reason we aren't taking action is because we don't understand the magnitude of the problem, what is that magnitude? Dr. Chu pointed us here towards the Stern Review and certain parts of the IPCC that have gone unnoticed and underappreciated. According to these sources, an increase of 2-3°C (3.6-7.2°F) means significant changes in water availability, a doubling of damage costs from hurricanes in the United States, a possible collapse of the Amazon rainforest, and failing crops and increased hunger around the world.[3] Those scenarios are projected for the 450-650 ppm C0₂e range; researchers say that we are already at the equivalent of 430 ppm.[4]

In addition, global emissions levels may actually be increasing faster than scientists expected. The Washington Post recently announced that in 2007 emissions outpaced the IPCC's worst business as usual predictions, putting us on track for temperature increases of more than 6.1°C by the end of the century.[5] And making all of this more likely are the numerous and often overlooked feedback effects that intensify and accelerate these changes. Can we really be apathetic to that?

Moreover, despite all the press to the contrary, Dr. Chu repeatedly reminded us that the IPCC reports are conservative documents. The consensus-seeking process of writing by committee used by the IPCC results in only using information and accepting conclusions that are beyond reproach. As a result, the "alarming" conclusions in the document tend to underestimate changes that will occur in a warmer world. Objections from China and Saudi Arabia caused a statement that the impact of human activity on the Earth's heat budget exceeds that of the sun by fivefold to be dropped – despite the fact that, according to a lead author, the difference is really a factor of ten.[6]

Thawing of the Permafrost – a Double Dose of Carbon

During our conversation with Dr. Chu, he directed us towards certain aspects of climate change that he believed were extremely important but underrepresented in the press. Feedback mechanisms came up multiple times in the conversation, due to their potential to speed up climate change and create a situation where we lose our ability to keep up and respond. It is a problem that future IPCC studies will need to better understand. Could the Earth's response to global warming itself cause additional global warming?

More specifically, Dr. Chu talked about the thawing of Arctic permafrost. Permafrost covers 22% of exposed land in the arctic and boreal regions of the Northern Hemisphere, and remains frozen for years at a time. The permafrost contains more than twice the carbon present in the atmosphere today. As global temperatures increase, the permafrost thaws, and the carbon trapped in its soils becomes the food of microbes and bacteria. In turn, those microbes emit carbon dioxide into the atmosphere. So as the permafrost thaws, a massive store of carbon could begin to enter the atmosphere, compounding the problems of climate change caused by human activity.

According to Dr. Chu, scientists aren't sure at exactly what temperature this process will accelerate, making it hard to attach probabilities or timescales to the problem. This was one of the reasons it was not highlighted in the IPCC report. But the decomposition resulting from thawing permafrost is one of the most significant potential feedbacks from terrestrial ecosystems to the atmosphere in a warming climate.

Here's how it works. Carbon is released into the atmosphere from thawing permafrost due to its decomposition by soil microbes, with instances of fire also playing an important role. Both of these processes, microbial decomposition and fire frequency, are predicted to accelerate in a warmer climate. While mechanisms such as increased plant growth and changes in albedo can partially offset some effects of thawing permafrost on climate, the loss of carbon to the atmosphere is likely to represent a substantial source of additional carbon emissions over the next century.

Global warming will result in a net loss of permafrost on both regional and global scales. Experts have projected a release of 0.5-1 Pg of carbon per year from permafrost zone ecosystems. This forecast is similar in magnitude to carbon emissions from the much more publicized process of land-use change, which is estimated to be 1-2 Pg carbon per year. [7]

Unfortunately, predicting accurately the magnitude and effect of thawing permafrost is extremely difficult. Yet, experts estimate that up to 100 Pg of carbon could be released from thawing permafrost by the end of the century. This amount is roughly 17 times larger than current American annual CO₂ emissions, and approximately equivalent to 100 years of Indian emissions at present levels. Others have calculated a potential release of 40 Pg of carbon over four decades if 10% of the carbon stock in Siberia thawed to 5°C, or 48 Pg C from Canadian permafrost over the course of the century if average air temperature increased by 4°C.[8]

Global circulation models are just starting to incorporate simple permafrost dynamics, but cannot completely and accurately calculate the carbon cycle in thawing permafrost. This means that the threat of thawing permafrost, despite its potential to release huge amounts of greenhouse gases into the atmosphere, has gone largely unnoticed and underappreciated. And it's not the only such effect to slide in under the radar.