Global temperatures have increased by almost a degree since pre-industrial times, and it is clear that human greenhouse gas emissions have been the primary driving force behind this temperature increase. However, the sources of these emissions have and continue to vary dramatically between regions and individual countries, with countries in the developed world responsible for the vast majority of historical emissions. While some rapidly developing countries have begun to overtake developed countries in terms of current emissions – China, for example, is now the largest national emitter of carbon dioxide – there remains a general pattern of disparity between countries in the developed and developing world with respect to total historical emissions, and consequent contributions to observed global warming.
Abstract
There is considerable interest in identifying national contributions to global warming as a way of allocating historical responsibility for observed climate change. This task is made difficult by uncertainty associated with national estimates of historical emissions, as well as by difficulty in estimating the climate response to emissions of gases with widely varying atmospheric lifetimes. Here, we present a new estimate of national contributions to observed climate warming, including CO2 emissions from fossil fuels and land-use change, as well as methane, nitrous oxide and sulfate aerosol emissions While some countries‘ warming contributions are reasonably well defined by fossil fuel CO2 emissions, many countries have dominant contributions from land-use CO2 and non-CO2 greenhouse gas emissions, emphasizing the importance of both deforestation and agriculture as components of a country’s contribution to climate warming. Furthermore, because of their short atmospheric lifetime, recent sulfate aerosol emissions have a large impact on a country’s current climate contribution We show also that there are vast disparities in both total and per-capita climate contributions among countries, and that across most developed countries, per-capita contributions are not currently consistent with attempts to restrict global temperature change to less than 2 °C above pre-industrial temperatures.
National contributions to observed global warming
There was a concerted recent attempt to quantify the contributions of individual countries to historical warming, as part of the MATCH network (the ad hoc Group for the Modelling and Assessment of Contributions to Climate Change—www.match-info.net). This group of researchers produced several papers (den Elzen and Schaeffer 2002, den Elzen et al 2005, Höhne et al 2010, Ito et al 2008) the most recent of which (Höhne et al 2010) represents a detailed analysis of the many uncertainties associated with determining historical national emissions of carbon dioxide, methane and nitrous oxide, as well as the difficulty in translating those emissions into national contributions to global temperature increases. This body of literature reveals several remaining challenges associated with attributing historical warming to individual countries: (1) regional data on historical emissions of CO2 from land-use and land cover change are highly uncertain (Houghton 2008), and not easily downscaled to the resolution of individual countries; (2) CO2 and non-CO2 greenhouse gases vary greatly in their atmospheric residence times (Solomon et al 2010), and as such it is not clear how to best compare the climate effects of historical emissions of short- versus long-lived gases; and (3) national aerosol emissions have thus far been neglected, despite the fact that they represent an important contribution to observed climate change. {jathumbnail off images="images/content_01_2014/erl483242f1_hr.jpg"}
In this paper, we present a new analysis of national contributions to observed global warming incorporating the most important greenhouse gas and aerosol emissions—carbon dioxide, methane, nitrous oxide and sulfate aerosols—that have driven global warming over the past two centuries. For CO2 emissions, we have used the linear relationship between cumulative emissions and global temperature change (Matthews et al 2009) to allocate warming to individual countries based on cumulative historical emissions. For CO2 emissions from land-use and land cover change, we have developed a new method to assign cumulative historical emissions to individual countries based on observed changes in forested areas within countries. We have also incorporated a novel approach for representing the effect of short-lived greenhouse gas and aerosol emissions, wherein we have allocated temperature change to each country based on a calculation of cumulative national historical emissions that is weighted according to the atmospheric lifetime of the temperature response to each type of emission. This new methodology allows for an improved national attribution of historical temperature changes, which incorporates the warming influence of emissions of CO2 (from both fossil fuels and land-use) methane and nitrous oxide, as well as the cooling effect of sulfate aerosols.
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Planning and Environment, Department of Geography, Concordia University, Canada
H Damon Matthews damon.matthews@concordia.ca et al 2014 Environ. Res. Lett. 9 014010
doi:10.1088/1748-9326/9/1/014010
© 2014 IOP Publishing Ltd
