“Magic Number” for safe warming

Presently, majority has been agreed to 2 degree Celsius, though the warming of 1.5 degrees posses high threats to earth climatic system

“Deciding what level of warming is dangerous and what level is safe is not a scientific question. It depends on the level of it involves the normative and political judgment about the acceptable risk.” (2009 State of the world into Warming World p-18). No level of warming is suitable for the earth ecosystem, though the third assessment report, more recent scientific developments and most of the countries joined in calling for global mean warming limited to 2 degrees. At the same time some least developed countries and small Island developing states have been arguing for warming far below 2 degrees for their guaranteed safety. In 2007 paper, NASA climate scientist James Hansen and his colleague argued for a limit of 1.7 degrees Celsius above preindustrial.   Other climate scientist Danny Harvey of the University of Toronto has said that even the present concentration of GHGs may constitute dangerous threats for the earth climatic system.  This would mean the warming should be limited below 1.3-1.4 degrees Celsius above the preindustrial level for “safe” planet, give that the present GHGs levels would likely warm the planet by about this amount once the world ocean and climate system fully respond to this concentration.

Presently, majority has been agreed to 2 degree Celsius, though the warming of 1.5 degrees posses high threats to earth climatic system.  Between the warming of 1.5 -2.0 degree Celsius, for instance, 10-15 % species are committed to extinction , Glacier in the Himalayan region and Tibetan plateau  could be reduced by 80%, adversely affecting the billions of people, up to additional 3 million people will be affected by Increased damage from storms and flood. So, there is no any “magic number” that would limit the warming to safe level with high confidence below 2 degree Celsius.

Scientists talk about the several potential climate stabilization levels that could help minimize the negative effects of climate change.   Policy makers really around these different stabilization points, using them to develop policies to rein in green house gas emission. But not everyone agree on the same stabilization points, and recent studies indicate that the level may need to be lower than once believed.

Potential stabilization points	Details
Global temperature increase of 2 degree Celsius	According to IPCC, the risks and threats of climate change increase dramatically when global temperature rise more than 2 degree Celsius. Government leaders and nongovernmental organizations have embraced2 degree as the maximum rise allowable if the worst effect of the climate change is to be avoided.
Global Green House Gas reduction of 15-20 % below baseline level within the next 10-20 years.	Reduction needed to limit global temperature rise to 2-3 degree Celsius, according to the IPCC. To achieve this goal CO2 levels must peak by 2015-20 and then fall
Atmospheric CO2 at 350 ppm	NASA climate scientist James Hansen and his colleague argue that many global warming tipping points have already been passed. Although current concentration of CO2 in the atmosphere exceed 380 parts per million, these scientists believe atmospheric concentration needs to drop to 350 ppm or lower as soon as possible.
Atmospheric CO2 at 450-550 ppm	U.K economist Nicholas stern advises that the uppermost stabilization level for atmospheric concentration of CO2 should not exceed 450-550 ppm in order to avoid global economic collapse . Based on climate models, this stabilization point takes into account prediction about technological developments and the time needed for widespread action.

References:

“Risk of Climate Change Damage Would be reduced by Stabilizing CO2 Concentration” , in IPCC, Climate Change 2001. Synthesis report (Cambridge, U.K.: Cambridge University Press 2001); IPCC, op. cit. note 1, p. 67: James Hansen et al., ” Target Atmospheric CO2: where should Humanity Aim?” Open Atmospheric Science Journal, 2008; “Towards a goal for Climate Change Policy,” in Nicholas Stern, The Economics of Climate Change: The Stern Review (Cambridge, U.K. :), Hare W.L. (2009). A Safe Landing for the Climate Change. 2009 State of the world into Warming World (p 20-21). 500 Fifth Avenue, New York, NY 10110