Sunday, January 11, 2015

Half a Degree and Harvest Failure. Why We Need to Understand Climate Change

In his January 8th Albuquerque Journal essay on climate, George Will made two major points. One, that since climate varies naturally, humans cannot be "primary disruptors of climate normality". There is a fallacy here: because climate varies without our help doesn't mean we can’t have an important impact. Mr. Will discusses historical climate change and the impact even minor climate variations have on human civilization,  noting that temperature changes as small as half a degree centigrade can determine crop success or failure. Because small changes in climate can have large impacts on critical human activities, we need to study and understand climate, and all the influences causing its change.

Climate responds to how much heat the earth receives from the Sun, to how much of that heat the planet retains, and to how it is distributed on the earth.  Variations in solar output (often correlated to sunspot cycles), wobbles in the Earth's orbit (Milankovich cycles), slow changes in the arrangements of the continents and oceans due to plate tectonics, eruptions of volcanoes that release climate-impacting particles and gases to the atmosphere, and variations in how ocean currents and water masses (i.e., the Gulf Stream, Japan Current, El Nino/Southern Oscillation) distribute heat to the planet influence global climate. The chemical makeup of the atmosphere controls how it retains or loses heat to space, acting as a giant radiator. In essence, its a complicated system; these processes work on different time scales and to make matters interesting, there are feedback loops between these processes.

The reason we worry about using fossil fuels is that when they are burned, they release their carbon as carbon dioxide (CO2). CO2, as well as water vapor and methane,  are important "greenhouse" or Tyndall gases. These gases, because of their molecular structures, absorb and re-radiate to the atmosphere infrared energy that would otherwise simply escape back to space, an effect studied since the early eighteen hundreds by scientists including Joseph Fourier, Svante Arrhenius, and John Tyndall. Moving large quantities of carbon as CO2 to the atmosphere from carbon sources long buried in the earth makes humans agents of climate change. This is because we are changing the atmosphere's effectiveness in retaining more of the Sun's energy. Some estimate that without any Tyndall gases in the atmosphere, the earth's climate would be some tens of degrees colder. We have, in a little over a hundred years, increased the atmospheric concentration of CO2 by some forty percent and we are not slowing down. Sixty to seventy percent of the Earth’s greenhouse warming is due to water vapor while carbon dioxide provides just a few degrees (NASA's Cosmos). But as Mr. Will reminds us, a few degrees can be profound. Both cooling and heating of the earth impact human and biological activities, weather patterns, and sea level.

Our ability since the Industrial Revolution to change atmospheric chemistry and thus the atmosphere's ability to retain the sun's heat, in a nutshell, is why humans can profoundly (at least with respect to our own existence) impact climate. Since as Mr. Will tells us, even small changes in climate can be the difference between feast and famine, we really do need to recognize two things. One, humans influence climate, and I've just described one important way in which we do so. There are others; not all might produce warming. Two, we need to understand how the Earth works and how we impact it if we are to manage rather than react to change, sometimes feasting, sometimes starving, often not knowing what to expect next.

This was published in the 25 January 2015 Albuquerque Journal, complete with the original comma splices.... 
Judy Curry on climate: WSJ: The global warming statistical meltdown.

Climate Heretic: Judith Curry Turns on her Colleagues (Sci American, reprinted in Nature)