Category: Earth Observation

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Imagine the year 2065. Two-thirds of Earth’s ozone is gone. The infamous ozone hole over Antarctica is a year-round fixture with a twin over the North Pole. People living in mid-latitude cities like Washington, D.C., get sunburned after five minutes. DNA-mutating UV radiation is up 650 percent, with likely harmful effects on plants, animals and human skin cancer rates.

Such is the world we would have inherited if 193 nations had not agreed to ban ozone-depleting substances, according to atmospheric chemists at NASA, Johns Hopkins University in Baltimore and the Netherlands Environmental Assessment Agency in Bilthoven. The researchers have unveiled new computer simulations this week of a worldwide disaster that humans managed to avoid.

In retrospect, the researchers say, the Montreal Protocol was a “remarkable international agreement that should be studied by those involved with global warming and the attempts to reach international agreement on that topic.”

Ozone is Earth’s natural sunscreen, absorbing and blocking most of the incoming UV radiation from the sun and protecting life from DNA-damaging radiation. The gas is naturally created and replenished by a photochemical reaction in the upper atmosphere where UV rays break oxygen molecules into individual atoms that then recombine into three-part molecules (O3). As it is moved around the globe by upper level winds, ozone is slowly depleted by naturally occurring atmospheric gases. It is a system in natural balance.

But chlorofluorocarbons — invented in 1928 as refrigerants and as inert carriers for chemical sprays — upset that balance. Researchers discovered in the 1970s and 1980s that while CFCs are inert at Earth’s surface, they are quite reactive in the stratosphere (10 to 50 kilometers altitude, or 6 to 31 miles), where roughly 90 percent of the planet’s ozone accumulates. UV radiation causes CFCs and similar bromine compounds in the stratosphere to break up into elemental chlorine and bromine that readily destroy ozone molecules. 

In the 1980s, ozone-depleting substances opened a wintertime “hole” over Antarctica and opened the eyes of the world to the effects of human activity on the atmosphere.  In January 1989, the Montreal Protocol went into force, the first-ever international agreement on regulation of chemical pollutants.

In the new study, published online in the journal Atmospheric Chemistry and Physics, Goddard scientist Paul Newman and his team simulated “what might have been” if chlorofluorocarbons (CFCs) and similar chemicals were not banned. The simulation used a comprehensive model that included atmospheric chemical effects, wind changes, and radiation changes. The “World avoided” video can be viewed here in Quicktime (for more formats, go here).

By the simulated year 2020, 17 percent of all ozone is depleted globally. An ozone hole starts to form each year over the Arctic, which was once a place of prodigious ozone levels.

By 2040, global ozone concentrations fall below the same levels that currently comprise the “hole” over Antarctica. The UV index in mid-latitude cities reaches 15 around noon on a clear summer day, giving a perceptible sunburn in about 10 minutes. Over Antarctica, the ozone hole becomes a year-round fixture.

By the end of the model run in 2065, global ozone drops 67 percent compared to 1970s levels. The intensity of UV radiation at Earth’s surface doubles; at certain shorter wavelengths, intensity rises by as much as 10,000 times. Skin cancer-causing radiation soars.

“Our world avoided calculation goes a little beyond what I thought would happen,” said Goddard scientist and study co-author Richard Stolarski, who was among the pioneers of atmospheric ozone chemistry in the 1970s. “The quantities may not be absolutely correct, but the basic results clearly indicate what could have happened to the atmosphere.”

“We simulated a world avoided,” added Newman, “and it’s a world we should be glad we avoided.”

As it is, production of ozone-depleting substances was mostly halted about 15 years ago, though their abundance is only beginning to decline because the chemicals can reside in the atmosphere for 50 to 100 years. The peak abundance of CFCs in the atmosphere occurred around 2000, and has decreased by roughly 4 percent to date. Stratospheric ozone was depleted by 5 to 6 percent at middle latitudes, but has somewhat rebounded in recent years.

Responding to a deadly 1997 outbreak of the mosquito-borne disease Rift Valley fever, researchers had developed a “risk map,” pictured above, using NASA and National Oceanic and Atmospheric Administration measurements of sea surface temperatures, precipitation, and vegetation cover. As reported in a recent NASA-led study, the map gave public health officials in East Africa up to six weeks of warning for the 2006-2007 outbreak of the deadly Rift Valley fever in northeast Africa — enough time to lessen human impact.

On the map above, pink areas depict increased disease risk, while pale green areas reflect normal risk. Yellow dots represent reported Rift Valley fever cases in high-risk areas, while blue dots represent occurrences in non-risk areas. The researchers have detailed the map’s effectiveness in the Proceedings of the National Academy of Sciences.

During an intense El Niño event in 1997, the largest known outbreak of Rift Valley fever spread across the Horn of Africa. About 90,000 people were infected with the virus, which is carried by mosquitoes and transmitted to humans by mosquito bites or through contact with infected livestock. That outbreak prompted the formation of a working group — funded by the U.S. Department of Defense Global Emerging Infections Surveillance and Response System — to try to predict future outbreaks.

The working group didn’t start from scratch. The link between the mosquito life cycle and vegetation growth was first described in a 1987 Science paper by co-authors Kenneth Linthicum of the U.S. Department of Agriculture and Compton Tucker of NASA’s Goddard Space Flight Center. Later, a 1999 Science paper described a link between Rift Valley fever and the El Niño-Southern Oscillation, a cyclical, global phenomenon of sea surface temperature changes that can contribute to extreme climate events around the world.

Building on that research, Assaf Anyamba of NASA Goddard and the University of Maryland, and his colleagues, set out to predict when conditions were ripe for excessive rainfall — and thus an outbreak. They started by examining satellite measurements of sea surface temperatures. One of the first indicators that El Niño will boost rainfall is a rise in the surface temperature of the eastern equatorial Pacific Ocean and the western equatorial Indian Ocean. Perhaps the most telling clue is a measure of the mosquito habitat itself. The researchers used a satellite-derived vegetation data set that measures the landscape’s “greenness.” Greener regions have more than the average amount of vegetation, which means more water and more potential habitat for infected mosquitoes. The resulting risk map for Rift Valley fever, showing areas of anomalous rainfall and vegetation growth over a three-month period, is updated and issued monthly as a means to guide ground-based mosquito and virus surveillance.

As early as September 2006, the monthly advisory from Anyamba and colleagues indicated an elevated risk of Rift Valley fever activity in East Africa. By November, Kenya’s government had begun collaborating with non-governmental organizations to implement disease mitigation measures—restricting animal movement, distributing mosquito bed nets, informing the public, and enacting programs to control mosquitoes and vaccinate animals. Between two and six weeks later—depending on the location—the disease was detected in humans.

After the 2006-2007 outbreak, Anyamba and colleagues assessed the effectiveness of the warning maps. They compared locations that had been identified as “at risk” with the locations where Rift Valley fever was reported. Of the 1,088 cases reported in Kenya, Somalia, and Tanzania, 64 percent fell within areas delineated on the risk map. The other 36 percent of cases did not occur within “at risk” areas, but none were more than 30 miles away, leading the researchers believe that they had identified most of the initial infection sites.

The potential for mapping the risk of disease outbreaks is not limited to Africa. Previous research has shown that risk maps are possible whenever the abundance of a virus can be linked to extremes in climate conditions. Chikungunya in east Africa and Hantavirus and West Nile virus in the United States, for example, have been linked to conditions of rainfall extremes.

“We are coming up on almost 30 years of vegetation data from satellites, which provides us with a good basis for predicting,” said Linthicum, co-author on the 1987 paper, upon his return from a Rift Valley fever workshop in Cairo, Egypt last month. “At this meeting, it was clear that using this tool as a basis for predictions has become accepted as the norm.”

Sources: NASA and the Proceedings of the National Academy of Sciences