1997 6.9 Practical implications
1998 The United Nations Framework Convention on Climate Change (UNFCCC, 1992) states:
1999 “The ultimate objective of this Convention and any related legal instruments that the
2000 Conference of the Parties may adopt is to achieve, in accordance with the relevant
2001 provisions of the Convention, stabilization of greenhouse gas concentrations in the
2002 atmosphere at a level that would prevent dangerous anthropogenic interference with the
2003 climate system. Such a level should be achieved within a time frame sufficient to allow
2004 ecosystems to adapt naturally to climate change, to ensure that food production is not
2005 threatened and to enable economic development to proceed in a sustainable manner.”
2006 “Dangerous” is not further defined by the Convention. Our present paper has several
2007 implications with regard to the concerns that the Framework Convention is meant to address:
2008 First, our conclusions suggest that a target of limiting global warming to 2°C, which has
2009 sometimes been discussed, does not provide safety. We cannot be certain that multimeter sea
2010 level rise will occur if we allow global warming of 2°C. However, we know the warming would
2011 remain present for many centuries, if we allow it to occur (Solomon et al., 2010), a period
2012 exceeding the ice sheet response time implied by paleoclimate data. Sea level reached +6-9 m in
2013 the Eemian, a time that we have concluded was probably no more than a few tenths of a degree
2014 warmer than today. We observe accelerating mass losses from the Greenland and Antarctic ice
2015 sheets, and we have identified amplifying feedbacks that will increase the rates of change. We
2016 also observe changes occurring in the North Atlantic and Southern Oceans, changes that we can
2017 attribute to ongoing warming and ice melt, which imply that this human-driven climate change
2018 seems poised to affect these most powerful overturning ocean circulation systems, systems that
2019 we know have had huge effects on the planetary environment in the past. We conclude that, in
2020 the common meaning of the word danger, 2°C global warming is dangerous.
2021 Second, our study suggests that global surface air temperature, although an important
2022 diagnostic, is a flawed metric of planetary “health”, because faster ice melt has a cooling effect
2023 for a substantial period. Earth’s energy imbalance is in some sense a more fundamental climate
2024 diagnostic. Stabilizing climate, to first order, requires restoring planetary energy balance. The
2025 Framework Convention never mentions temperature – instead it mentions stabilization of
2026 greenhouse gas concentrations at a level to avoid danger. It has been shown that the dominant
2027 climate forcing, CO2, must be reduced to no more than 350 ppm to restore planetary energy
2028 balance (Hansen et al., 2008) and keep climate near the Holocene level, if other forcings remain
2029 unchanged. Rapid phasedown of fossil fuel emissions is the crucial need, because of the
2030 millennial time scale of this carbon in the climate system. Improved understanding of the carbon
2031 cycle is needed to determine the most effective complementary actions. It may be feasible to
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2032 restore planetary energy balance via improved agricultural and forestry practices and other
2033 actions to draw down atmospheric CO2 amount, if fossil fuel emissions are rapidly phased out.
2034 Third, we not only see evidence of changes beginning to happen in the climate system, as
2035 discussed above, we have associated these changes with amplifying feedback processes. We
2036 understand that in a system that is out of equilibrium, a system in which the equilibrium is
2037 difficult to restore rapidly, a system in which major components such as the ocean and ice sheets
2038 have great inertia but are beginning to change, the existence of such amplifying feedbacks
2039 presents a situation of great concern. There is a possibility, a real danger, that we will hand
2040 young people and future generations a climate system that is practically out of their control.
2041 We conclude that the message our climate science delivers to society, policymakers, and
2042 the public alike is this: we have a global emergency. Fossil fuel CO2 emissions should be
2043 reduced as rapidly as practical.
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