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Special Edition 2016 Quarterly Science Supplement

Ten Key Points: Global Warming and Greenhouse Gases
1.     Concentration of CO2 now exceeds 400ppm – a 43% increase over pre-industrial levels.
2.     Non-CO2 GHGs in 2015, tracked by NOAA’s Annual Greenhouse Gas Inventory, increase warming by a factor of 1.37 to a CO2 equivalent of 485 ppm.
3.     The Earth’s global average surface temperature has warmed over 1°C since the 1880s; 2016 is likely to be the hottest year in the 136-year record.
4.     Since 1975 the rate of global temperature increase has been 0.18°C per decade.
5.     Industrial era ocean heat content has doubled since the late 1990s.
6.     There is an improved understanding of how natural cycles such as the Interdecadal Pacific Oscillation and other processes can amplify or dampen anthropogenic warming on interannual to decadal timescales.
7.     A recent climate sensitivity study of the response to a doubling of CO2 of past climates finds that the temperature response is more sensitive during warm interglacial periods, such as the present.
8.     Natural gas-related methane emissions from the fossil fuel industry are 20 to 60 percent greater than EPA and European Commission estimates.
9.     Modeled projections of sea level rise from past assessments are on the low side of observations.
10.  To achieve the less than 2°C Paris Agreement goal, there is a likely need for technologies that can achieve negative emissions unless substantial reductions occur before 2050.  

Since the 1980s a vast amount of research from both the modeling and observation communities have focused on how the Earth system will respond to human activity, and in turn, how humanity and ecosystems will be affected. The climate change component of humankind’s footprint has been codified in numerous scientific assessments including the flagship reports of the Intergovernmental Panel on Climate Change (IPCC), which are developed about every 6 years under the auspices of the United Nations Environmental Programme and World Meteorological Organization. Each of the IPCC assessments has built upon the growing knowledge base that increasingly refines the detection of climate change in greater detail and with deeper understanding of the underlying processes. The confidence that detected changes are attributable to human causes has steadily grown with each assessment. With the improving ability to observe and model the Earth, the confidence in the bottom-line statements about climate change have become more exacting.

Models and observations will likely continue to improve as more processes in the highly complex Earth system become better represented; however, the evidence of human influence is clear and mounting – not only in the temperature record, but in many aspects of the Earth system such as sea level rise, loss of sea ice, change in precipitation patterns, ocean acidification, and altered ecosystems. From a cumulative carbon budget standpoint, to avoid 2°C change, the window is closing. Longer delays in decreasing annual emissions, require a steeper rate of carbon reductions and potentially carbon removal. Meanwhile, societal and ecosystem impacts—principally from sea-level rise, heat stress, altered precipitation, and ocean acidification—are already present: their detrimental impacts will continue to accelerate, absent swift and sustained global response.

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