What Americans Urgently Need to Understand About Climate Change In Light of an Alarming New Report Published By US Academy of Sciences


On July 31, 2018, a paper was published in the Proceedings of the National Academy of Sciences which should create a shiver of fear in all humans everywhere. The paper, Trajectories in the Earth System in the Anthropocene by Steffen et..al., explains how human-induced warming is rapidly approaching levels that may trigger positive climate feedbacks which could greatly accelerate the warming already plaguing the world by causing record floods, deadly heat waves and droughts, increasing tropical diseases, forest fires, more intense and damaging storms, sea level rise, coral bleaching, acidification of oceans, all of which are contributing to increasing the number of refugees which are destabilizing governments around the world.

The Steffen et. al. paper also describes how the positive feedbacks depicted in the following graphic, once triggered could initiate other feedbacks creating a cascade of positive feedbacks, each of which could speed up the warming which is already causing great harm and suffering around the world. The paper claims this mechanism could make life on much of the Earth uninhabitable which could lead to social collapse on the global scale and ultimately to warming increases that human reductions of greenhouse gases (ghg) emissions alone would not prevent until the global system reached a new temperature equilibrium at much higher temperatures than the human race has ever experienced. In other words, cascading positive feedbacks in the climate system could result in humans losing control over reducing disastrous warming.

Image result for global map of tipping cascades

Steffen et. al,, supra pg. 4.

If this is not scary enough, the Steffen et. al. paper concluded some of these feedbacks could be triggered between 1 degree C to 3 degrees C, suggesting that the “risk of tipping cascades could be significant at a 2 degree C rise (Steffen at al p.7), the upper warming limit goal of the Paris Agreement which President Trump has announced the United States will withdraw from.

Given that even if temperature increases already baked into the system don’t trigger positive feedbacks until global temperatures rise by 2 degrees C and given the enormous challenge facing the world to achieve the 2 degrees C warming limit goal agreed to by the international community in Paris in 2015 requires the international community to achieve net zero CO2 emissions by 2070 (UNEP, Emissions Gap, 2016), the international community needs to immediately join forces to achieve extraordinarily ambitious international cooperation almost immediately to achieve the 2 degree C warming limit goal. However, given that the 2 degree C warming limit goal agreed to in Paris was selected because it was believed that if warming increases could be limited to 2 degrees C, triggering dangerous climate system positive feedbacks was unlikely, the conclusions of the Steffen et al paper that positive feedbacks could be triggered below 2 degrees C additional warming must be interpreted as a justification for a call for an unprecedented urgent global cooperative effort to reduce carbon emissions and increase carbon sinks as rapidly as humanly possible.

Given that human-induced climate change is now widely understood to be an existential threat to life on Earth unless all nations rapidly reduce their greenhouse gas (GHG) to net zero as fast as possible, Americans urgently need to understand certain features of the problem which have been infrequently mentioned in the US national climate change conversation including the following: 

  • There is growing evidence that even if global ghg emissions could be reduced to near zero rapidly, there is enough carbon already in the atmosphere that limiting warming to the then 2 degrees C warming limit goal by the end of this Century has only a 5% chance (Mooney, 2017).
  • Every day that nations fail to reduce their GHG emissions to levels required of them to achieve a warming limit goal such as 2 degrees C makes the problem worse because budgets available for the whole world that must constrain global emissions to achieve any warming limit goal shrink as emissions continue. Therefore, the speed that nations reduce their GHG emissions reductions is as important as the magnitude of reductions identified by any national GHG reduction commitment. For this reason, any national commitment on climate change should not only identify the amount of ghg emissions that will be reduced by a certain date, but the reduction pathway by which these reductions will be achieved,
  • For reasons stated in the Seffen et.al. paper, climate change is an existential threat to life on Earth that requires the international community to rapidly take extraordinarily aggressive coordinated steps not only sufficient to prevent global temperatures from rising no than more than 2 degrees C, the upper warming limit agreed to by the international community in the 2015 Paris Agreement, but to minimize any additional warming as quickly as possible,
  • Under the United Nations Framework Convention on Climate Change (UNFCCC) which the US ratified in 1992, the US has a legal duty under the concept of “equity” to reduce its GHG emissions more rapidly than most other nations, and although there is reasonable disagreement among nations about what “equity” requires of them, any reasonable interpretation of equity would require the US to make much larger and more rapid GHG reductions than almost all other nations given that the United States emitted 5,011,687 metric kilo tons (kt) of CO2 equivalent emissions in 2016, second only to China’s 10,432,741 kt CO2. (Netherlands Environmental Agency). The US also has an equitable duty to more aggressively reduce its emissions than most other countries because it has emitted a greater amount of cumulative CO2 emissions, that is 29.3% of global CO2 emissions between 1850 and 2002, while China emitted 7.6% during the same period, (WRI, Cumulative Emissions) making the US much more responsible for raising atmospheric concentrations of CO2 to the current level of 406 ppm than any country.  Also given the US is responsible for 15.56 metric tons per capita CO2 emissions which is more than twice as much as China’s 7.45 metric tons per capita in 2016 (World Bank), as a matter of equity the US must reduce its GHG emissions much more rapidly and steeply than almost all countries,
  • The US duty to formulate its ghg emissions reduction target on the basis of equity is not only required by its legal obligations under the UNFCCC, practically the US and other high emitting nations must reduce their GHG emissions by much greater amounts and faster than poor developing nations because if they don’t the poorer nations will have to reduce their GHG emissions almost immediately to near zero CO2 so that global emissions don’t exceed the carbon budget available to prevent a warming limit such as 2 degrees C from being exceeded,
  • Any US policy response to climate change such as a carbon tax must be structured to reduce US ghg emissions to levels and speeds required of the US to achieve its responsibilities to the rest of the world to prevent dangerous climate change. Thus, if the US were to pass a carbon tax, the imposition of a tax must either reduce US GHG emissions to the level and the speed required of it by its obligations or be supplemented by other policy responses such as, for instance, mandatory conversions of electric power generation from fossil fuel combustion to renewable energy by a date certain or mandatory requirements for electric vehicles,
  • Because GHG emissions from every country mix rapidly in the atmosphere, all nations emissions are contributing to rising atmospheric GHG concentrations thus harming people and ecological systems on which life depends all over the world. Thus, the US may not formulate its climate change policies only on the basis of costs and benefits to itself alone, it must acknowledge and respond to the devastating climate change harms the United States is already contributing to that are being experienced around the world and particularly by poor people and nations that are most vulnerable to climate change impacts. For this reason, the Trump administration’s justification for withdrawing from the Paris Agreement on the basis of “putting US interests first” is deeply morally indefensible and tragic because of the damage it will likely cause to the world,
  • Because of the rapid speed required of the US to reduce its ghg emissions to net zero carbon emissions, the US urgently needs to put ghg emissions reductions on the equivalent of a wartime footing by not only adopting policy responses that can achieve ghg emission reduction goals required of it, but also by investing in research and development in new technologies that can facilitate and achieve the its ghg emission reduction obligations and increase carbon sinks that could reduce the rise in atmospheric ghg concentrations,
  • The United States needs to develop a strategy to achieve these objectives in the next two years and begin implementing the strategy immediately as quickly as possible.


Donald A. Brown

Scholar in Residence and Professor

Widener University Commonwealth Law School