A few weeks ago an independent team of scientists funded by a prominent foundation announced to great twitter, "Global warming is real." The news itself wasn't surprising to anyone close to the problem; this is something the rest of the scientific community has known for two decades. But the source of the news was noteworthy: one lead scientist of the study was a self-proclaimed climate skeptic, and the study was funded in part by the Charles G. Koch Foundation, which, among other things, has funded efforts to derail climate-related state legislation.
This team duplicated earlier studies that showed the Earth has warmed by about 1 degree C (1.8 degrees F) since the 1950s. The present decade is the warmest in over two centuries. Earlier allegations that climate scientists conspired to manufacture data were, and still are baseless. This new result confirms the point and "leaves little room for doubters," as The Economist neatly summarized.
This warming trend presents real and present risks to things that really matter: the security of food, water, and land. Most people are not gravely concerned that global temperature will be X degrees warmer in the coming decades. But rising temperature is a harbinger of associated risks to things we utterly depend upon as individuals and nations.
Food. Crop yields decrease by about 10% for every 1°C of warming. The reduced yield is due to crop stunting during extreme heat events -- and these will increase in frequency as climate warms up. A recent analysis showed that the hottest seasons presently on record for the breadbasket regions of the world will become the seasonal norm by the end of the 21st century. For reference, the severe drought and heat wave that struck Texas this summer caused $5 billion in combined agricultural and livestock losses. A separate but related issue is that fish provide roughly one-quarter of the world's protein. Ocean acidification due to human carbon emissions impacts the growth of marine plankton that form the base of the food chain.
Water. One of the real power plays in future climate change involves changes in access to water. Under greater greenhouse gas emission scenarios, climate models consistently show a tendency for wet regions to become wetter, and dry regions to become drier and to expand. For the semi-arid expanses of the American West and northern Mexico, for example, climate change will establish a new climate, with annual water availability reduced by amounts equivalent to those seen in the historic droughts of the 1930s and 1950s. Warming and moistening of the atmosphere is also expected to lead to more intense weather and climate extremes -- more heavy rainstorms, more floods and more droughts. In addition, more of the very strongest and most destructive hurricanes are expected.
Land. About 10% of the world's population lives within 10 meters elevation of the coastline. Sea-level response to a warming world remains one of the more vexing quantities to estimate, but the average estimates are about one-half meter rise by the end of this century. But that estimate does not account for melting ice sheets. Recent observations show that both the Greenland and West Antarctic ice sheets are disintegrating at record paces. Each ice sheet represents the equivalent of roughly 5 to 7 meters of potential sea level rise. Coastal cities will battle floods from storms and tidal surges as average sea levels creep higher.
Climate and life have been intertwined throughout Earth's history. Seasons pace the cycle of death and renewal; the diversity of life is highest in the warm tropics; and taking the longest possible view, each of the "big five" mass extinctions of life on Earth (times when over 50% of animal species became extinct) were each associated with environmental crises.
Climate change modifies humanity's access to food, water, and land, and it does so with cruel inequality. Developed nations responsible for most of the carbon emissions have a surfeit of food, water, and, in North America, space, but the rest of the world lives in constant, acute need of these. They have done little to cause the problem of climate change but will suffer the most -- an environmental injustice on a planetary scale.
It's time to shift the discussion to what people hold dearest, for these are the things in play in the coming decades. We evidently agree now that global warming is real. Now, it's time to move on and discuss what's really at stake. As the world population passes 7 billion, it is imperative to advance the discussion beyond a simple chart of Earth's surface warming to illuminate our true concern -- the security of food, water, and the very land on which we live.
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