ccs_main The final thematic report from the Intergovernmental Panel on Climate Change on mitigation of climate change was launched this weekend (blog posts on the first two reports can be found here and here). This final report assesses the scientific, technological, environmental, economic and social aspects of mitigation of climate change. Mitigation being defined as ‘a human intervention to reduce the sources or enhance the sinks of greenhouse gases’.

The report paints a picture of where we are now in terms of emissions, possible emission reduction scenarios, mitigation options for different sectors and current strategies and plans for emission reductions.

Globally, greenhouse gas (GHG) emissions from human activities continue to grow. Total anthropogenic GHG emissions were the highest in human history from 2000 to 2010 and reached 49 (±4.5) giga tonnes of carbon dioxide equivalent per year (GtCO2eq/yr) in 2010. About half of all anthropogenic CO2 emissions (from 1750 to 2010) have been released in the last 40 years. The report notes that ‘without additional efforts to reduce GHG emissions beyond those in place today, emissions growth is expected to persist driven by growth in global population and economic activities’. Scenarios without additional mitigation result in global mean surface temperature increases in 2100 from 3.7 to 4.8 ºC compared to pre-industrial levels (median values – the full range is 2.5 to 7.8 ºC).

The report looked at around 900 mitigation scenarios – these spanned a wide range of mitigation outcomes from GHG concentration levels in 2100 from 430 ppm CO2eq to above 720 ppm CO2eq. The summary report focuses on those mitigation scenarios that likely, more likely than not, as likely as not, and more unlikely than likely keep temperature change to less than 2 ºC relative to pre-industrial levels. For these different types of likely to more unlikely, the scenarios are characterised by atmospheric concentrations of greenhouse gases in 2100 of about 450 ppm CO2eq, 500 ppm CO2eq, 530 ppm CO2eq and 530 to 650 ppm CO2eq, respectively. For context, the CO2eq concentration in 2011 was estimated to be 430 ppm.

The report does outline a huge variety of mitigation options across a wide range of sectors – buildings and urban areas, transport, industry, energy supply, agriculture and other land uses. Clearly, meeting the lower range of end of the century greenhouse gas levels requires more rapid implementation of these options. And, the bigger the delay in mitigation the more difficult it will be to reach these levels. A key message that comes through the report is that the more mitigation is delayed, the more costly it will be. In baseline, or business-as-usual, scenarios consumption grows by 1.6 to 3 % per year over the next century. High mitigation scenarios (in line with 2100 atmospheric CO2eq of 450 ppm) implemented immediately would result in a reduction of this growth by 0.04 to 0.14 (median: 0.06) percentage points a year. Delaying additional mitigation increases the costs in the medium to long term. It’s noted that these estimates don’t take into account the economic benefits of reduced climate change.

The opening paragraphs of the report outlines quite starkly why mitigation of climate change is needed: ‘Limiting the effects of climate change is necessary to achieve sustainable development and equity, including poverty eradication’.

It also highlights the need to develop and implement mitigation and adaptation policies in the context of broader development pathways so that mitigation efforts don’t undermine efforts towards sustainable development.

Comments from Royal Society Fellows on the newly released report can be found here and an In Verba assessment of the coverage of geoengineering in the report can be found here.

  • Mike Jonas

    Globally, annual greenhouse gas (GHG) emissions from human activities have been increasing for the last 30 years or more, and have nearly doubled over that period, yet there has been no statistically-significant global temperature increase in this millenium. This was NOT predicted by ANY of the climate models. Would the Royal Society now acknowledge that there could be just the teeniest little glimmer of doubt about the climate models and their predictions of global mean surface temperature increases in 2100 from 3.7 to 4.8 ºC, given that one seventh of the century has now passed with no statistically-significant surface temperature increase, and if anything there is an indication that the global surface temperature may have started to cool a little?