How Does Black Carbon Change the Climate Debate? [ PDF ]

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Arctic Amplification

Saya Kitasei, Climate Institute

The Arctic, an area with a small population and even smaller political influence, is also one of the most important – and the most vulnerable – to climate change. Research warns that the Arctic, with the rest of the planet in tow, could approach major tipping points within decades, allowing less time than we thought we had to act on global warming. If we are to prevent these outcomes, immediate and serious mitigations in carbon dioxide emissions must be complemented by reductions in short-lived warming agents such as black carbon and methane.

The Arctic is warming twice as fast as the rest of the planet. According to the Arctic Climate Impact Assessment, while global average surface temperatures rose 0.78˚C between 1890 and 2007, the Arctic warmed by a total of 1.9˚C (i). This breakneck warming is disrupting the delicate balance between ice, water, and sun in the Arctic – a balance which plays a vital role in maintaining the Earth’s climate as we know it.

The Arctic’s iconic sea ice and glaciers are vanishing. Peter Wadhams, a leading polar scientist from the UK, recently announced new evidence that the Arctic Ocean will be ice-free during the summer within twenty years (ii). The rapid decline in Arctic sea ice portends serious consequences for the entire climate system. This October, the National Oceanic and Atmospheric Administration’s Arctic Report Card noted that the loss of summer sea ice is affecting large scale wind patterns as well as Arctic plant, animal and fish species (iii). Scientists at Rutgers University and the University of Delaware warn that a warmer Arctic will affect weather throughout the Northern Hemisphere (iv).

As Arctic ice melts, it also contributes to sea level rise, a serious threat to small island and low-lying coastal populations as outlined by Tom Roper in this issue. The IPCC estimates that if the 2.9 million km3 of ice contained in the Greenland Ice Sheet melted, sea level would rise about 7.3 meters (v).

Because feedback loops in the Arctic amplify the effect of global warming, a destabilized Arctic could initiate dangerous chain reactions in the global climate system.

First, reduction in snow and ice cover accelerates warming. Some incoming solar radiation is reflected by the Earth, while the remainder is absorbed, warming the planet’s surface. Fresh snow and sea ice reflect 80-90 and 50-70 percent of incident sunlight, respectively, thereby helping to regulate the planet’s temperature (vi). As glaciers and sea ice retreat, they reveal much darker surfaces like bare soil or water, which reflect only a fraction of the light that snow and ice can. Thus as the Arctic warms and ice and snow melt, the Earth’s reflectivity, or albedo, decreases, driving further warming and further melting.

Second, higher temperatures could release large amounts of carbon dioxide currently stored in the Arctic Ocean and permafrost. This month, a joint study by the Arctic Monitoring and Assessment Program, the Climate in the Cryosphere Program, and the International Arctic Science Committee announced that the Arctic accounts for 10 to 15 percent of the global carbon sink (vii). Normal soils contain decomposing organic matter, which emits carbon dioxide, but permafrost, or permanently frozen soil, does not decompose – as long as it stays frozen. But warmer temperatures are causing permafrosts to thaw, and scientists worry that this large volume of ancient organic matter will resume en masse the carbon-emitting process of decomposition that has been on pause for thousands of years.

Finally, global warming is transforming once-frozen soils into waterlogged incubators for methane-producing organisms. The Arctic currently releases as much as 50 million metric tons of methane per year. Even higher emissions of methane, a greenhouse gas 23 times more potent than carbon dioxide, will significantly accelerate global warming by compounding the effects of carbon dioxide emissions. “If the response of the Arctic carbon cycle to climate change results in substantial net releases of greenhouse gases,” the study’s lead author warned, “this could compromise mitigation efforts that we have in mind for controlling the carbon cycle (viii).”

Black carbon plays a central role in Arctic warming and so must play a central role in preventing the Arctic from undergoing irreversible climate change. In a Nature Geoscience review published last year, Veerabhadran Ramanathan and Greg Carmichael conclude that the deposition of black carbon, which absorbs solar energy and heats the ice and snow below it, is responsible for 0.5 to 1.0˚C (or up to 50 percent) of temperature increase in the Arctic (ix). Even organic carbon, light-reflecting particles that tend to be emitted together with black carbon and normally mitigate the effect of black carbon by increasing albedo, is less reflective than snow cover and can contribute to local warming.

New atmospheric models reveal that black carbon emitted north of 40˚N is most likely to be transported to the Arctic. Thus while Europe, North America and the former Soviet Union are responsible for only about 17 percent of the world’s black carbon emissions (Europe: 7 percent; North America: 6 percent, former Soviet Union: 4 percent), these countries’ emissions have a disproportionate effect on the Arctic and, in turn, on the global climate (x). These countries have the resources and the responsibility to curb their black carbon emissions and protect the Arctic.

A great deal is at stake in the Arctic. The lifestyles of indigenous peoples, the health of local economies, and the survival of arctic species hang in the balance. But the Arctic also plays a major stabilizing role in the global climate system, and warmer temperatures in the Arctic will amplify existing climate impacts. Swift action to reduce black carbon and other short-lived greenhouse gases could prevent disastrous Arctic melting that would have ramifications across the globe.

Footnotes

(i) Arctic Council. (2005) Arctic Climate Impact Assessment. Cambridge University Press.

(ii) Peter Griffiths. (2009) “Arctic to be ice-free in summer in 20 years: scientist.” Reuters, October 15, 2009.

(iii) Richter-Menge, J., and J. E. Overland, Eds. (2009) Arctic Report Card 2009.

(iv) Morello, Lauren. (2009) “Experts see Arctic warming decades faster than models predict.” ClimateWire, October 1, 2009.

(v) Solomon, S., et al. (2007) Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK, p. 829.

(vi) Markvart, T., and Luis Castañer, Eds. (2003) Practical Handbook of Photovoltaics: Fundamentals and Applications. Elsevier Science, p. 60.

(vii) McGuire, A. David, et al. (2009) “Sensitivity of the carbon cycle in the Arctic to climate change.” Ecological Monographs, 79(4), 523-555.

(viii) Science Daily. (2009) “Arctic has potential to alter Earth’s climate: Arctic land and seas account for up to 25 percent of world’s carbon sink.” October 15, 2009.

(ix) Ramanathan, V. and G. Carmichael. (2008) “Global and regional climate changes due to black carbon.” Nature Geoscience, 221-7.

(x) Bice, K., et al. (2009) Black Carbon: A Review and Policy Recommendations. Woodrow Wilson School of Public and International Affairs. PDF

Autumn 2009 Climate Alert

How Does Black Carbon Change the Climate Debate? [ PDF ]

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