Obama Fights Global Warming
By Nayyer Ali MD
The recent announcement of even tighter CO2 emission standards for power plants by Obama has been met with outrage by the usual suspects. This is a necessary action as the Republicans have decided to deny that global warming is even a thing. There is clearly no point in trying to get legislation on this.
While most conservatives deny that global warming is even a problem, there are some on the left that go beyond what most scientists think and make wildly inflated claims of doom. As such I decided to go to the source document for the actual scientific consensus, which is the Fifth Assessment Report of the IPCC released in 2014. The IPCC is the Intergovernmental Panel on Climate Change, which was set up by the UN in 1990 to bring together the best understanding of this topic and provide governments the most complete picture of what carbon dioxide emissions will do to the planet. This is done through their periodic “Assessment Reports”. The most recent was the Fifth Assessment Report, which was released in 2014, and included a 65-page overall summary of the key points, entitled Climate Change 2014 Synthesis Report.
The IPCC begins by stating the warming in the last century has been unequivocal and unprecedented in the historical record. In the Northern Hemisphere the period 1983-2012 is very likely the warmest in the last 800 years, and probably the warmest in the last 1400 years. From 1880 to 2012 the global average temperature (GAT) has risen 0.85 degrees C. In the last 15 years the temperature has been rising at a rate of 0.05 degrees per decade. The recent rate of rise is very sensitive to the chosen start year (1997 vs 98 vs 99), this slow rate of rise in the last 15 years is most likely due to natural variability and does not mean that global warming has slowed.
In the last 100 years, 90% of excess heat has been stored in the oceans, 9% has ended up in the land and ice masses. Only 1% has ended up in the atmosphere. Average ocean temps have been rising by 0.11 degrees per decade since 1970.
Since 1990 there has been loss of ice mass in glaciers, Greenland ice cap, and the Antarctic ice cap. Maximum snow extent in the Northern Hemisphere in late winter has declined by 1.6% per decade since 1967.
Sea levels have been rising for 2000 years. The rate of sea level rise has accelerated since 1900, with a rise of 19 cm in the last hundred years (roughly 5 inches). In the last interglacial about 100,000 years ago, sea levels peaked between 5 and 10 meters higher than current, though average global temperatures were at least 2 degrees warmer than current for several thousand years.
With regards to the so-called “pause” in global warming, referring to the relatively slow rate of warming since about 1997, the IPCC states that they have “medium confidence” the pause is due to natural variability. They do note that of 114 climate simulations, the expected rise in temperature in the last 15 years was higher than the actual in 111 of the simulations. When looking at longer time periods, the models and actual values line up pretty well.
CO2 levels are rising at 2 ppm per year, other greenhouse gases particularly methane and nitric oxide also rising. CO2 persists in the atmosphere for many centuries, methane lasts 12 years and nitric oxide about 120 years. In a change from the Fourth Assessment Report, IPCC now concludes that aerosols have less of a net cooling effect than previously thought.
Since 1750, humans have emitted 560 gTC (gigatons of carbon), with annual emissions now running 9.5 gTC. The main drivers of increasing annual emissions are population growth and economic growth, though the IPCC does not assign relative responsibility.
The climate consequences of warming include increased frequency and severity of heat waves and precipitation events. In general, current wet regions are expected to get wetter, while current dry regions expected to get drier. Monsoonal systems (critical to agriculture and life across East Africa, South Asia, and East Asia) are expected to enlarge. Warming will not be uniform. Warming will be greater in the polar regions and also over land rather than ocean.
The risks of global warming are to both human civilization and the biosphere. For humans extreme weather events may cause significant disruptions. Poorer nations and regions will be impacted more severely due to lack of resources to mitigate effects. There will be significant costs associated with adaptation to or mitigation of global warming. There will be both increased water scarcity in arid regions, perhaps leading to conflicts, and increased incidence of flooding events.
Extinction rates are expected to increase but IPCC did not quantify this. Fisheries are expected to deplete in the tropics and increase in the temperate zones. Coral and polar ecosystems are at particular risk. Coral may be damaged by significant changes in ocean pH, while warming may substantially shrink or eliminate Arctic summer sea ice. Impacts will be substantially larger if warming exceeds 4 degrees. With that level of warming, the entire Greenland ice sheet could melt, though the melting process will take greater than 1000 years.
The IPCC concluded at this point there is no evidence of an Arctic sea ice “tipping point” when loss of albedo in the summer results in runaway melting and complete loss of the ice cap. Next week I will look at predictions that the IPCC makes, based on different future scenarios of low or high fossil fuel use.