Thanks to some ongoing research, mentioned below, the relationship between water and global warming is coming into sharper focus. Sadly for us, the picture we’re seeing as layers of uncertainty are peeled away is nothing to be cheerful about.
I’ve mentioned many times that the primary, near-term human impact of global warming will not be some ridiculously overblown instant climate catastrophe, as depicted in The Day After Tomorrow, or even swamped coastal cities (but that iconic danger has also taken a new turn, as one source below points out). Rather, we’ll see something much more subtle but every bit as dangerous: Shifts in precipitation patterns and temperatures that lead to some densely populated areas having much less water for drinking, crop irrigation, sanitation, and electricity generation. The two main mechanisms at work are as simple as they are devastating:
But the water/global warming relationship is more complex than that. Let me cite three recent articles as examples of how much we’re still learning about the role of water in our global climate:
Melting ice now main driver of rising sea levels: study:
Runoff from ice caps in Antarctica and Greenland along with melting mountain glaciers have replaced expanding oceans as the main driver of rising sea levels, according to a new study.
The rate at which the global ocean water mark rises could have a devastating impact on hundreds of millions of people living in low-lying areas around the world.
Earlier research had shown that sea levels crept up and average of 3.1 millimetres (0.12 inches) per year from 1993 to 2003.
More than half of that increase came from a process called thermal expansion whereby the ocean gains in mass as climate change pushes global temperatures upward.
The other half, climate scientists calculated, was caused by land ice, especially dwindling glaciers in mountain ranges such as the Himalayas and Andes.
The new study, drawing on data from two new observational systems, shows that thermal expansion — which is cyclical over periods measured in decades — essentially stopped after 2003.
But sea levels continued to rise, though at the slightly diminished rate of 2.5 millimetres (0.1 inches) per year.
Which left scientists wondering: if the water had stopped expanding, what was now driving the continuing elevation of the world’s oceans?
The answer, it turns out, are the only two masses of ice on Earth big enough to qualify as ice sheets: Greenland and Antarctica. Both are up to three kilometres (two miles) thick, and Greenland — the smaller of the two — is about the size of Mexico.
“During the last decade, Antarctica and Greenland only contributed about 0.5 mm (0.02 inches) per year to rising sea levels whereas today it is about 1.0 mm (0.04 inches) per year,” said Anny Cazenave, a scientist at France’s National Centre for Space Studies and lead author of the paper.
Water vapor confirmed as major player in climate change:
Water vapor is known to be Earth’s most abundant greenhouse gas, but the extent of its contribution to global warming has been debated. Using recent NASA satellite data, researchers have estimated more precisely than ever the heat-trapping effect of water in the air, validating the role of the gas as a critical component of climate change.
Andrew Dessler and colleagues from Texas A&M University in College Station confirmed that the heat-amplifying effect of water vapor is potent enough to double the climate warming caused by increased levels of carbon dioxide in the atmosphere.
With new observations, the scientists confirmed experimentally what existing climate models had anticipated theoretically. The research team used novel data from the Atmospheric Infrared Sounder (AIRS) on NASA’s Aqua satellite to measure precisely the humidity throughout the lowest 10 miles of the atmosphere. That information was combined with global observations of shifts in temperature, allowing researchers to build a comprehensive picture of the interplay between water vapor, carbon dioxide, and other atmosphere-warming gases. The NASA-funded research was published recently in the American Geophysical Union’s Geophysical Research Letters.
“Everyone agrees that if you add carbon dioxide to the atmosphere, then warming will result,” Dessler said. “So the real question is, how much warming?”
The answer can be found by estimating the magnitude of water vapor feedback. Increasing water vapor leads to warmer temperatures, which causes more water vapor to be absorbed into the air. Warming and water absorption increase in a spiraling cycle.
Water vapor feedback can also amplify the warming effect of other greenhouse gases, such that the warming brought about by increased carbon dioxide allows more water vapor to enter the atmosphere.
“The difference in an atmosphere with a strong water vapor feedback and one with a weak feedback is enormous,” Dessler said.
Study Examines Effects of Global Warming on Oceans:
Polar ice is part of a positive feedback loop that exacerbates climate changes. As temperature increases, ice melts. Since ice is white, Arctic melting decreases the reflectivity of the Earth. As a result, more solar radiation gets absorbed, further increasing temperatures and perpetuating the cycle. The opposite is true for temperature decreases.
According to the study, a new trend in Arctic melting is affecting the Atlantic Ocean. The primary change has been an abnormally large influx of water originating from the Pacific and traveling through the Arctic.
Water in the Pacific Ocean is less salty than water in the Atlantic. Approximately once every decade, some water from the Pacific travels through the Arctic and spills into the Atlantic.
However, in 1989, the freshwater infusion was more powerful than expected. Proposing that greenhouse gases were the main cause of this anomaly, Greene said, “Greenhouse gases are contributing to more fresh water in the Arctic Ocean [since global warming can lead to] greater precipitation, runoff, melting tundra and melting ice.”
The study identified two major symptoms of this change: a dramatic movement in the oceanic biosphere and a “regime shift” in the composition of Atlantic water.
The 1999 freshwater infusion had some peculiar characteristics. In May of that year, specimen of Neodenticula seminae, a species of boreal plankton, were detected in the Atlantic Ocean. N. seminae had been absent from the northern Atlantic fossil record for 800,000 years. However, since its discovery, the species has proliferated along the Eastern seaboard.
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Since the water remains stratified for longer, the Atlantic growing season has been extended. The study observed a recent surge in copepods, one of the main predators of phytoplankton.
However, not all species have benefited from this transition. The study hypothesized that the infusion of fresh Arctic water has played a role in the dramatic fall in cod stocks in the northwest Atlantic.
The study also discussed the effects of the regime shift on the global oceanic conveyor belt. Approximately 10 years ago, scientists seriously discussed the possibility of an extreme disruption in NADW possibly halting global heat redistribution. However, the study reported, “results from more recent climate change models have downplayed the likelihood of this scenario, at least in the near future … NADW formation and the global ocean’s [conveyor belt] are likely safe from abrupt change during the 21st century.”
However, Greene is cautiously optimistic. “A great reduction or even a complete shutting down of NADW formation [are] real possibilities in the coming centuries … change would likely be quite abrupt.”
In spite of the powerful implications of the study, Greene warned strongly against taking the study for more than it was worth. He criticized several publications for distorting or sensationalizing the point of the paper.
You can decide for yourself just how much good news or bad news is in these and similar news items regarding global warming, but the one inescapable conclusion I draw from them is that we’re continuing to tweak (or jostle or kick, depending on one’s views) our planet’s biosphere at a terrifying rate, given the nature of the discoveries we’re still making. Seems like something we should stop doing, doesn’t it?
I’ve just started reading Chris Wood’s Dry Spring: The Coming Water Crisis of North America. While I can’t provide a full review based on just the first two chapters, it seems to be a very good treatment of the topic for a mainstream audience.
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