* The term “ppm” stands for parts per million. This is a common gas concentration unit, and is a measure of the ratio of CO2 molecules to all other atmospheric molecules.
As the name suggests, global warming is an increase in the average global temperature due to a rise in atmospheric gases that absorb and store heat, known as “greenhouse gases.” The greenhouse gas that receives the most media attention is carbon dioxide (CO2), due to the drastic surge of CO2 in the atmosphere since the industrial revolution: as the figure below demonstrates, CO2 concentrations rolled gently around their historical norm of 290 ppm* until the 1900’s, when they began to clamber up their jagged summit of 390 ppm in 2000.1
Current CO2 concentrations are now up to 400 ppm. Less atmospherically abundant (and therefore less notorious) greenhouse gases store more heat — methane**, for instance, stores seven times more heat than CO2, and nitrous oxide stores 153 times more heat.2 All of these emitted greenhouse gases in the atmosphere sponge up heat from the sun, and a jump in greenhouse gas concentration leads to a warming of the global atmosphere.
** The normally less conspicuous methane may become more infamous in the near future, as natural gas is becoming a popular energy source.
This may bring to mind a better world where the mild, warm climate of Southern California is equally enjoyed by residents of Chicago and Milwaukee. But don’t throw your winter boots and down coat into a celebratory bonfire just yet. The copious greenhouse gas concentration in the atmosphere has boosted average global temperature by just 1˚F (or 0.6˚C)3.
More importantly, an increase in average global temperature will be accompanied by a wider range of temperatures, both hot and cold.4 Hot summer days will be hotter, and colder winter nights will be colder, and those lovely mild evenings will be fewer and farther in between. This horrible side effect is thanks to unpredictable cloud cover and rain/snow events that accompany that tiny 1 ˚F temperature boost. Common cures to woeful weather, such as a cooling rain in July or a sunny day in February, may become less frequent with global warming. It may be heartbreaking, but we will have to take the “mild” out of our future climate dreams.
*** Confused about the difference between climate and weather? That’s probably because it’s confusing. In short, climate refers to the average temperature, moisture, wind, and cloudiness across the globe for a long period of time, while weather refers to daily temperature, moisture, wind, and cloudiness in a region such as your neighborhood. So, climate = whole world, for a long, long time, and weather = here and now.
The ability of global warming to make the winters to feel colder is confusing. Even more confusing is the ability of a global warming to lead to baffling weather.*** That small 1 ˚F boost is felt by all the cogs and sprockets of Earth, such as ocean heat uptake, air and ocean currents, global ice volume, sea level, cloud coverage, and precipitation. This translates into some bewildering weather, such as more frequent floods in some regions, but more frequent droughts in other regions.4, 5 Some of these subtle effects are difficult to predict, such as cloud coverage and regional rain and snow. It’s these subtleties that lead to counterintuitive short-term weather. For instance, global warming may increased winter cloud cover, which combined with the already chilly temperature can actually lead to freezing events.6
Global warming is complicated; it makes my summers hotter and my winters colder, and I hate it. At least I still have you, ice cream.
1. Rackley, S. A., Carbon Capture and Storage. 2010. ↩
2. http://en.wikipedia.org/wiki/Greenhouse_gas ↩
3. Easterling, D. R.; Meehl, G. A.; Parmesan, C.; Changnon, S. A.; Karl, T. R.; Mearns, L. O., Climate extremes: Observations, modeling, and impacts. Science 2000, 289 (5487), 2068-2074. ↩
4. Meehl, G. A.; Karl, T.; Easterling, D. R.; Changnon, S.; Pielke, R.; Changnon, D.; Evans, J.; Groisman, P. Y.; Knutson, T. R.; Kunkel, K. E.; Mearns, L. O.; Parmesan, C.; Pulwarty, R.; Root, T.; Sylves, R. T.; Whetton, P.; Zwiers, F., An introduction to trends in extreme weather and climate events: Observations, socioeconomic impacts, terrestrial ecological impacts, and model projections. Bulletin of the American Meteorological Society 2000, 81 (3), 413-416. ↩
5. Coumou, D.; Rahmstorf, S., A decade of weather extremes. Nature Climate Change 2012, 2 (7), 491-496. ↩
6. Karl, T. R.; Trenberth, K. E., Modern global climate change. Science 2003, 302 (5651), 1719-1723. ↩
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