(As an introduction, Dr. Carroll said that environmental science, unlike biomedical research, is not dominated by a single powerful entity like “big pharma,” the major drug manufacturers. The challenge in the environmental field is that political pressure sometimes determines what kinds of explanations the public receives from federal agencies such as the Environmental Protection Agency or the National Aeronautics and Space Administration. Academic scientists working in the field, however, have more freedom to translate science for reporters and the public.)
Consequences of global warming
The current concentrations of key greenhouse gases (carbon dioxide, methane, nitrous oxide) and their rates of change are unprecedented. These gases are responsible for trapping energy in the earth’s atmosphere; the consequence of this is a rise in temperature, or global warming.
We know empirically that 85% of world’s glaciers are retreating. This is not a series of data points: there are huge consequences. Three quarters of the world population depend on melt from glaciers. As the glaciers run dry, there are gigantic consequences. Ice caps in Greenland and the Antarctic are melting twice as fast as expected.
[When you are reporting on the environment my advice is to] think globally—write locally. Consider global connections and their impact on your local setting to give [your audience] a sense of context. Remember that science is not just a list of facts—it is a trajectory toward understanding.
Hurricanes are an example. Our “old” understanding of hurricanes was that Georgia was protected by the “bight” – the state’s concave coastline. Our new understanding tells us that the path of hurricanes is determined by the Bermuda High—the same high-pressure cell that gives us hot, muggy August and September days.
Our old understanding was that global warming would make hurricanes stronger and more frequent. Now, we know that global warming is likely to influence wind shear and dust from Africa (among other things) that actually weaken hurricanes. Our best current understanding is that hurricanes may become less frequent, but those that do occur will be stronger.
Wind shear will become more common in Atlantic basin. Dust clouds blowing off Mali are sucking energy out of hurricanes. The dust clouds are related to the long-term aridity of the area and the tendency of people settling and overgrazing from their livestock. So, as the goat population grows in Mali, hurricane activity diminishes in Georgia!
So, what does that mean to us in Georgia, those of us who live below the “gnatline”? It means less drought relief in the summer and fall, and fewer, but more severe storms.
How does global warming affect us in terms of waterborne illness?
As global warming increases, we will tend to increase water use. We both increase the problem and our vulnerability to global warming.
For example, our housing density in the United States in 1940 was almost at maximum for water use—use and capacity for waste handling. Something has to happen.
As we use more fresh water and load water with more waste, we increase the concentration of pathogens, and the nutrients that support them, in our water supply. This increases our vulnerability [to disease].
Climate change in Georgia, as a result of global warming, will result in changes. Changes that we know for certain are that sea levels will rise (possibly as much as a 1 meter rise within 40 years), many salt marshes will deteriorate, and the ecological and economic damage will be significant. The combination of tidal pulse and sea-level change will result in an increase in water on coastlines, with the resultant deterioration of ecologically important salt marshes.
These changes in water level are very visual. Reporters can show readers and viewers what this will look like.
Climate change also affects river flow. Likely changes—and ones worth worrying about—are that summer river flow will drop and some will run dry, so that new diseases will emerge.
The drought of 2006 is an example. In the middle of May, the Middle Oconee River was running full. As the drought developed through the summer, the water flow went down to less than 1 cubic foot per second. That resulted in many isolated pools, little oxygen in the water, and low flow during the hottest time of the year.
Recurrent droughts like this create a dim future for Georgia’s cold-water fish. Global warming is expected to eliminate as much as 75% of trout fishing in Georgia over the next several decades.
Why do waterborne pathogens love global warming?
Some pathogens (salmonella, cholera) like warm water and survive longer in it. Food supplies are more concentrated for both pathogens and vectors, such as mosquito larvae. And the low amount of oxygen in water means fewer predators, especially fish that eat mosquitoes.
Global warming and human health
Four examples will serve to illustrate the impact of global warming on diseases and environmental hazards that can affect health here in Georgia.
West Nile virus gives us a glimpse into the future for more diseases related to global warming.
Birds are the most important reservoir for this virus, and humans and farm animals are just incidental hosts. However, there have been 15,000 cases of human disease in the United States since 1999, and more than 500 deaths. In 2007, we had 50 cases in Georgia with one death. The consequences can be bad even for people who survive, as many are left with long-time neurological disorders.
The West Nile virus will continue because the mosquitoes (vectors) love warm, nutrient rich water without fish—a global warming contribution. Also the common bird hosts maintain high levels of the virus, resulting in greater levels of transmission.
Moreover, the growing demand on aging waste water treatment plants means that more sewage is dumped into rivers and is concentrated during droughts—mosquitoes love this!
But here in Georgia, we are missing key information. Only 28 counties routinely survey for infected mosquitoes, and only 7 counties recorded West Nile positive mosquitoes. The number of counties conducting surveillance for West Nile has dropped from 60 counties in 2004. So, as the disease is getting more common, surveillance is going down.
Beyond West Nile, we have to be concerned about Dengue fever—a rapidly emerging disease. There is no cure and no vaccine.
The primary mosquito vectors are Aedes aegypti and Aedes albopictus (Asian tiger mosquito); the latter mosquito has swept through Georgia, replacing other mosquitoes. It is very promiscuous and is a day-time biter.
In general, mosquitoes are affected by temperature. Just as little as a 2 degree rise means that the disease transmission period is almost year-round.
Toxic algal bloom is another problem. Cyanobacteria ( blue-green algae) flourish in warm, nutrient rich waters. Some species of cynaobacteria produce toxic compounds that are highly stable. Spraying with herbicides for other waterweeds releases cynobacterial blooms.
There is no monitoring of these algal blooms—zero database. We only know about the dead zones in the Gulf of Mexico due to run-off from coastal Mississippi. The resulting “red tides” or “black clouds”kill fish in the Gulf.
Toxic dust clouds are composed of toxic chemicals, fecal dust, pathogens—they are blowing in the wind.
Air pollution in China is very serious. In 75% of year, the air in Beijing is so bad that, if this city were in the United States, the EPA would recommend that people stay indoors. Dust clouds coming from China blows across our whole country. Dust includes bacteria and fungi; it is carried all around the world and is still viable.
In conclusion:
- We see more waterborne health risks as a result of global warming.
- New diseases are emerging.
- Aging water treatment plants can’t cope with the problems.
- Risk is increasing while surveillance in decreasing.
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