I just finished reading the National Climate Assessment’s Appendix on the science of climate change, and man, is it a bummer. Despite that, I am extremely happy I took the time to read it, and I think its totally worth an hour of time to review this appendix. The authors make a very clear case for the role of human activities in climate change, what this means for our planet so far, and what it could mean for the future.
For my own edification and memory of what I’ve read, I have gone ahead and selected some quotes and figures out of this Appendix that I think are particularly stark and compelling. Bear with me as I run through some of the major points, as follows:
“The human-induced increase in atmospheric levels of carbon dioxide and other heat-trapping gases is the main reason the planet has warmed over the past 50 years and has been a contributor to climate change over the past 150 years or more.”
“Carbon dioxide levels in the atmosphere are currently increasing at a rate of 0.5% per year. Atmospheric levels reached 392 parts per million in 2012, higher than anything the Earth has experienced in over a million years. Globally, over the past several decades, about 80% of carbon dioxide emissions from human activities came from burning fossil fuels, while about 20% came from deforestation and other agricultural practices…About 45% of the carbon dioxide emitted by human activities in the last 50 years is now stored in the oceans and vegetation. The remainder has stayed in the atmosphere, where carbon dioxide levels have increased by 40% relative to pre-industrial levels. ”
“Human-induced emissions of carbon dioxide have already altered atmospheric levels in ways that will persist for thousands of years. After a hundred years, about one third of the carbon dioxide emitted is still in the atmosphere. Methane lasts for approximately a decade before it is removed through chemical reactions. Particles, on the other hand, remain in the atmosphere anywhere from a few days to several weeks. This means that the effects of any human actions to reduce particle emissions can be seen nearly immediately. It may take decades, however, before the results of human actions to reduce long-lived greenhouse gas emissions can be observed.”
“Two important natural external drivers also influence climate: the Sun and volcanic eruptions. Since 1750, these natural external drivers have had a net warming influence, but one that is much smaller than the human influence.”
“By 2100, additional emissions from human activities are projected to increase CO2 levels 420 ppm under lower emissions (the RCP 2.6 scenario, which would require substantial emissions reductions) and 935 ppm under higher emissions (the RCP 8.5 scenario, which assumes continued increases in emissions). ” The report later goes on to show this latter level of emissions associated with a 10 to 12° F rise in average global temperature.
“While surface air temperature is the most widely cited measure of climate change, other aspects of climate that are affected by temperature are often more directly relevant to both human society and the natural environment. Examples include shorter duration of ice on lakes and rivers, reduced glacier extent, earlier melting of snowpack, reduced lake levels due to increased evaporation, lengthening of the growing season, and changes in plant hardiness zones. Changes in these and many other variables are consistent with the recent warming over much of the United States. Taken as a whole, these changes provide compelling evidence that increasing temperatures are affecting both ecosystems and human society. “
What is extraordinarily clear to me from reading these statements is 1) human activities are the primary cause of dramatic increases in heat-trapping gasses in our atmosphere 2) increases in emissions are going to continue to occur EVEN IF we take meaningful steps now to reduce our emissions and 3) I sure as hell don’t want to live, or want my child to live, in a world at 935 ppm CO2e. This is a call to action, people, and its never been clearer that we have got some major moving and shaking to do not to end up on the upper end of these very scary and very massive changes in the way our planet functions and supports us.