2 degrees is too high ! IPCC, United Nations, May 2015
Report on the structured expert dialogue on the 2013–2015 review, 4 mai 2015
While the data show that we would follow the current scenario of global warming estimated up to 6 degrees relative to the pre-industrial era (read this article, reference NASA), the latest discussions between the experts of the UN, members of the IPCC, the World Meteorological Organization and the Hadley Center seem to conclude that the value of 2 degrees of warming would not be a safe limit. From 1.5 degree, climate change would already enter a nonlinear evolution stage, with irreversible global effects, particularly hostile to life as a whole.
The Earth’s atmosphere is 0.85 degree hotter than during the pre-industrial times, and estimates of climate inertia (the time the atmosphere takes to react to more CO2) appear to indicate that even if we stop all CO2 emissions immediately, the 1.5 degrees of warming would be met or exceeded.
Page 98 : “(…) the Party* pointed out that four out of the five RFCs** show that the impacts of climate change increase in a non-linear fashion between 1.5 °C and 2 °C, especially for unique and threatened systems (e.g. the massive loss of coral reefs), large-scale singular events (e.g. the disintegration of ice sheets in Greenland and Antarctica in this warming range), or impacts on local agriculture.”
Page 98 : “For 1.5 °C warming scenarios, the required mitigation action in 2030 is very different from the action required for 2 °C warming scenarios.”
Page 104 : “(…) emission scenarios that limit temperature increase from preindustrial levels to below 2 °C require considerably different investment patterns during the period 2010–2029, including a fall in investments in fossil-fuel plants without CCS*** of USD 30 billion, an increase by USD 147 billion in investment in low-emission generation technologies, and an increase by USD 336 billion in energy-efficiency investments in the buildings, transport and industry sectors.”
Page 108 : “However, the IPCC repeatedly emphasized that their hands are tied, pointing out that scientific insights on the 1.5 °C limit are limited since results of the needed research are not yet available or not of the same robust nature as those on the 2 °C long-term global goal.”
Page 111 : “The first message was on the nature of the 2 °C and 1.5 °C limits to global warming. He emphasized that at SED 2, SED 3 and SED 4-1****, many experts, notably from the IPCC, had explained that climate-related impacts are prevalent at the current degree of warming of 0.85 °C above the pre-industrial level and have increasingly significant adverse effects, and that additional magnitudes of warming will only increase the risks of severe, pervasive and irreversible impacts. He stressed that this is an indication that any upper limit for global warming can no longer be seen as a guardrail providing protection from dangerous anthropogenic interference, and called for a consideration of societally, or otherwise, acceptable risks of climate impacts.”
Page 118 : “In a world 1.5 °C warmer than in pre-industrial times, we are on the verge of moving to high risk for these organisms, while in a world 2 °C warmer than in pre-industrial times, the risk already becomes high for these ecosystems. For freshwater and terrestrial species, in a world 1.5 °C warmer, most trees and herbs would be at moderate risk from falling behind the moving climate zones. However, in flat landscapes, 2 °C warming means that climate change velocity would become too high for terrestrial and freshwater organisms to follow the moving climate zones.“
* Party : one of the signatories of the the United Nations Framework Convention on Climate Change (UNFCCC).
** RFC : five reasons for concern, “which illustrate the implications of warming and of adaptation limits for people, economies and ecosystems across sectors and regions (figure 4, panel A)”, page 9.
*** CCS : Carbon Capture and Storage
**** SED : Structured Expert Dialogue