At my recent American Meteorological Society conference in Nashville, I was privileged to attend a day long short course on climate change (I’ve completed several such courses), led by several of the nation’s most accomplished climate scientists. This intense and amazingly inclusive day included basic and more advanced materials on what we know–and what we don’t know–about climate change and global warming. (The scholars lecturing included Deke Arndt, Chief of the Climate Monitoring Branch of NOAA’s National Climatic Data Center; Dr. Tony Broccolli, atmospheric scientist and Director of the Rutgers Climate and Environmental Change Initiative, and Chief Editor of the Journal of Climate; Harold Brooks, reseach meteorologist and Senior Scientist in the Forecast Research and Development Division at NSSL, the National Severe Storms Laboratory; Dr. Keith Dixon, research meteorologist and climate modeler at the NOAA Geophysical Fluid Dynamics Laboratory/GFDL in Princeton; Dr. Ben Santer, physicist and atmospheric scientist at the Lawrence Livermore National Laboratory, University of California; and Marshall Shepherd, AMS President and Department Chair of the University of Georgia’s Atmospheric Sciences Program.)
A few basics: CO2 is indisputably a greenhouse gas, which traps heat which would otherwise radiate back into space. Without water vapor and CO2, the earth would be a frozen ball. The basic physics are known, and not in dispute. CO2 has been increasing since the dawn of the industrial revolution. The burning of fossil fuels produces CO2. The increase has now taken us to 400 parts per million in the atmosphere, the highest level in at least 800,000 years and probably more than 1 million years.
Other greenhouse gases such as methane, also increasing, are much stronger as greenhouse gases. But the sheer volume of CO2 has far outstripped the capacity of methane in warming capacity. In addition, CO2 has a long, stable shelf life in the atmosphere once it’s released. Methane, which may increase more rapidly due to the melting of the Arctic permafrost and the possible release from slowly warming seabeds, has a life of just 14 years in the atmosphere.
The worst news is that a large portion of the past and future warming will be largely irreversible for at least a couple of centuries, due to that CO2 shelf life, and projected increases in CO2 from economic growth in nations such as China and India. (The US CO2 output has decreased significantly in recent years, due to the recession and even more so due to the lower cost of natural gas vs. coal and oil. Natural gas emits only 40% of the CO2 produced from burning coal.) But there is still good evidence that the size and effects of the warming can be mitigated to some extent by some element of reduction in the burning of fossil fuels. The mitigation involves social and political issues which I will not get into, since I have no more expertise on those topics than any of you…I’ll try to stick to the science.
The warming is “nonlinear” in that it will occur at an uneven pace. There can be embedded within the long term warming cooler periods, and some periods in which warming accelerates. Such a chart looks “spikey” with ups and downs, while the median continues to inexorably climb. We have, in fact, seen a slowing of the warming between 2000-2010. The best theoretical evidence on what caused that slowdown involves the oceans acting as a carbon and heat sink. That is, the ocean has been taking up a good deal of the extra carbon in the atmosphere (leading to acidification of sea water, having increased about 30% in recent decades) and the extra heat in the atmosphere. As seas have warmed, sea levels continue to rise even while atmospheric warming has temporarily slowed. Water expands as it warms, and there have been huge depositions of freshwater from the melting of the Greenland glaciers and most glaciers around the world. The reduction in arctic sea ice (the greatest) and antarctic sea ice secondarily has increased the ability of the high latitude seas to absorb more solar energy and warm, as well. Ice reflects solar energy. Dark sea water absorbs it. Global warming has been greatest in the Arctic region, just as climate models have predicted. At some point, the ocean’s capacity to absorb heat and carbon will begin to level off, and atmospheric warming will begin to accelerate again. The “spikey” appearance of global average temperatures can be easily observed in this graph: http://www.ncdc.noaa.gov/sotc/service/global/global-land-ocean-mntp-anom/201201-201212.png
One more basic: the evidence that human activity is responsible for the majority of global warming is overwhelming. There are more than 20 climate models, each of which can be run with different initial conditions. Every one of them when run with CO2 levels as they were known to be around 1900 show the world would have been cooling since that time. Even when natural warming forcing agents (solar input, for example) are maxed out during this time span up to the present, it is now known the globe would have been cooling on average without the human induced increase in greenhouse gases. In other words, the earth’s natural cycle at this time in its history would have been to enter a cooling period, were it not for us. Those who say “man is too puny to affect the climate” simply don’t grasp the basic, proven physics. Of course, the ultimate runaway greenhouse gas planet–with no help from civilization–is Venus. Its atmosphere is more than 90% CO2, and its surface temperature is over 900 degrees F–hot enough to melt lead. While there is zero chance than can happen here, it should at least demonstrate to those that CO2 is quite a greenhouse gas. Even strong denialists who have the mistaken idea we cannot really impact climate should at least notice the urban heat island effect. Urban areas have significantly higher temperatures day and night because of the absorbing and retaining of solar heat in concrete and pavement. On a clear night, my car themometer often drops 10-13 degrees by the time I get to my suburban home in a more rural section of my town compared to the temperature of north Buffalo. Because man’s urban heat island effect is so strong, these urban temperatures are NOT included in global temperature averages, so as not to skew the data.
Thanks for reading this far. I wanted to write this while the material is still fresh in my head. If this topic doesn’t hold much interest for you, feel free to comment on the weather. “Climate is what you expect. Weather is what you get.”