2671. Fertilizer from Industrial Agriculture Pollutes the Ocean

By Tatiana Schlossberg, The New York Times, July 27, 2017

Caused by chemical fertilizer use by American industrial agriculture, the Gulf of Mexico dead zone is one of the largest in the world. 

Nitrogen-based fertilizers, which came into wide use after World War II, helped prompt the agricultural revolution that has allowed the Earth to feed its seven billion people.

But that revolution came at a cost: Artificial fertilizers, often applied in amounts beyond what crops need to grow, are carried in runoff from farmland into streams, lakes and the ocean. New research suggests that climate change will substantially increase this form of pollution, leading to more damaging algae blooms and dead zones in American coastal waters.

A study published Thursday in Science concludes that eutrophication, excessive nutrient enrichment, is likely to increase in the continental United States as a result of the changes in precipitation patterns brought by climate change. Heavier rains caused by warmer temperatures will cause more agricultural runoff, sluicing more nutrients into rivers, lakes and oceans.

The authors found that future climate change-driven increases in rainfall in the United States could boost nitrogen runoff by as much as 20 percent by the end of the century.

“When we think about climate change, we are used to thinking about water quantity — drought, flooding, extreme rainfall and things along those lines,” said Anna Michalak, a professor of global ecology at the Carnegie Institution for Science in Stanford, Calif., and one of the authors of the study. “Climate change is just as tightly linked to issues related to water quality, and it’s not enough for the water to just be there, it has to be sustainable.”

Excess nitrogen from the fertilizers can cause eutrophication in the ocean, which can lead to harmful algae blooms or hypoxia — reduced levels of oxygen that create conditions in which organisms can’t survive.

The study’s authors looked at three emissions scenarios — high, stable and falling — in both the near and far future in more than 2,100 “subbasins” or watersheds in the continental United States.

Their results show that in the high emissions scenario, which assumes that future greenhouse gas emissions trends follow those of the past, increased precipitation alone would cause “large and robust increases” in nitrogen amounts on the watershed scale, particularly in the Upper Mississippi Atchafalaya River Basin, the Northeast, and the Great Lakes basin.

In the stable emissions model, in which a rise in global surface temperatures by two degrees Celsius from preindustrial times is more than likely, the Northeast would still see a robust increase in nitrogen loading.

This is in part because the nitrogen accumulation will occur in areas that already are experiencing it, and because watersheds in the Northeast and elsewhere drain into coastal regions where nitrogen pollution is already affecting water quality, the study said.

For instance, the Chesapeake Bay has experienced a “dead zone,” a result of hypoxia, regularly since 1950. Earlier this summer, the National Oceanic and Atmospheric Administration predicted a larger than average dead zone there, despite previous efforts at reducing nutrient levels.

The most notorious dead zone in the country surrounds the mouth of the Mississippi River in the Gulf of Mexico, which this year is expected to cover an area approximately the size of Vermont, nearly 10,000 square miles, according to research from Louisiana State University.

While the researchers did not specifically model the global effects of climate change on nitrogen loading in other parts of the world, they applied their models to analogous areas outside the United States. They found that large areas of East, South and Southeast Asia may experience increases in nitrogen levels similar to those seen in the United States.

Because these regions are home to more than half of the world’s population and are heavily dependent on surface water, the authors write, the effects of increased eutrophication are likely to be stark, turning the green revolution rather brown.

Farmers and agricultural authorities must take account of climate change and the prospect of increased rainfall in designing strategies to mitigate the effects of nutrient pollution. Otherwise, Ms. Michalak said, “They’re going to fail.”

2670. Summers Are Getting Hotter

By Nadja Popovich and Adam Pearce, The New York Times, July 28, 2017 

Summer temperatures
in the Northern Hemisphere

Extraordinarily hot summers — the kind that were virtually unheard-of in the 1950s — have become commonplace.

This year’s scorching summer events, like heat waves rolling through southern Europe and temperatures nearing 130 degrees Fahrenheit in Pakistan, are part of this broader trend.

The chart above, based on data from James Hansen, a retired NASA climate scientist and professor at Columbia University, shows how summer temperatures have shifted toward more extreme heat over the past several decades.

To create the bell curves, Dr. Hansen and two colleagues compared actual summer temperatures for each decade since the 1980s to a fixed baseline average. During the base period, 1951 to 1980, about a third of local summer temperatures across the Northern Hemisphere were in what they called a “near average” or normal range. A third were considered cold; a third were hot.

Since then, summer temperatures have shifted drastically, the researchers found. Between 2005 and 2015, two-thirds of values were in the hot category, and nearly 15 percent were in a new category: extremely hot.

Practically, that means most summers are now either hot or extremely hot compared with the mid-20th century.

1951 to 1980

2005 to 2015

1951-1980

Base period

More frequent

Hot

Normal

Extremely cold

Cold

Normal

Extremely hot

Extremely cold

Cold

Hot

Extremely hot

The big increase in summer temperatures under the dark red category of extreme heat is “right in line” with what scientists expect to see as the climate warms over all, said Todd Sanford, director of research at Climate Central, a nonprofit science and news organization.

For each time period above, the distribution of summer temperatures forms what is known as a bell curve because most measurements fall near the average, forming the bump – or bell – in the middle. More extreme temperatures, which happen less frequently, fall in the wings, with heat waves on the right and cold-snaps on the left.

As the curve’s average – the top of the peak – shifts rightward over time, more temperatures in more places end up in the hot and extremely hot categories and fewer end up in the cold category.

Dr. Hansen’s curves also flatten out, which some have suggested is an indication of greater temperature variability. But other climate scientists, including Zeke Hausfather, an energy systems analyst at the University of California, Berkeley, have pointed out that this effect is mainly a reflection that some parts of the world are warming faster than others. There is no evidence that temperatures are becoming more variable in most parts of the world after warming has been accounted for.

Dr. Hansen’s data “really highlight that changes in the average, while they may seem modest, have big implications for the extremes. And that’s what’s going to affect society and ecosystems,” Dr. Sanford said. The findings reveal what has happened so far, and also provide “a glimpse to what’s in our future.”

Source: Columbia University Earth Institute. Data via Makiko Sato and James Hansen. Based on: Hansen et al., 2012 (and discussion); 2016 update.

Temperature categories are determined by the normal distribution, so that a third of temperatures fall in each of the main three categories: hot, cold and normal for 1951 to 1980. Summer temperatures for each subsequent 11-year period are compared to the 1951 to 1980 baseline.