By Alex Kirby
Sea-level rise may be slow to show its hand but once it really starts, researchers say, it will keep going for centuries, with baleful effects. For each degree by which the Earth warms, they believe, sea levels will probably rise by over two meters.
Some recent research has suggested that the future rate of sea-level rise may not be as fast as scientists had expected. But a study published in the Proceedings of the National Academy of Sciences, The multi-millennial sea-level commitment of global warming, paints a different picture.
Today’s greenhouse gas emissions will cause sea levels to rise for centuries to come. “CO2 [carbon dioxide], once emitted by burning fossil fuels, stays an awful long time in the atmosphere,” says Anders Levermann, lead author of the study and research domain co-chair at the Potsdam Institute for Climate Impact Research in Germany. “Consequently, the warming it causes also persists.”
The oceans and ice sheets are slow to respond to warming, simply because of their enormous mass, which is why observed sea-level rise is now measured in millimeters per year. But once they start responding, they are unrelenting.
“The problem is: once heated out of balance, they simply don’t stop,” says Levermann. “We’re confident that our estimate is robust because of the combination of physics and data that we use.”
The study is the first to combine evidence from the Earth’s early climate history with comprehensive computer simulations using physical models of all four major contributors to long-term global sea-level rise.
Correctly Estimating Future Rise
During the twentieth century, sea level rose by about 0.2 meters, and it is projected at the moment to rise by significantly less than two metes by 2100, even under the most far-reaching scenarios considered.
But the researchers say past climate records, which average sea-level and temperature changes over a long time, suggest much higher sea levels during periods of Earth history that were warmer than at present.
For this study, the international team used data from sediments from the sea bottom and ancient raised shorelines found on coastlines around the world. All the models are based on fundamental physical laws.
“The Antarctic computer simulations were able to simulate the past five million years of ice history, and the other two ice models were directly calibrated against observational data—which in combination makes the scientists confident that these models are correctly estimating the future evolution of long-term sea-level rise”, says Peter Clark, a palaeo-climatologist at Oregon State University, U.S., and co-author of the study.
While it remains a challenge to simulate rapid ice loss from Greenland and Antarctica, the models are able to capture ice loss that occurs on long time scales where the research team says a lot of the small rapid motion averages out.
If global average temperature rises by 4 degrees Celsius compared with pre-industrial times, which in a business-as-usual scenario is projected to happen within less than a century, the Antarctic ice sheet will contribute about 50 percent of sea-level rise over the next two millennia.
“Continuous sea-level rise is something we cannot avoid unless global temperatures go down again. Thus we can be absolutely certain that we need to adapt”
The researchers say that while thermal expansion of the ocean (the way warmer water expands) and melting mountain glaciers are the most important factors causing sea-level change today, the Greenland and Antarctic ice sheets will be the dominant contributors within the next two millennia.
Half of that rise might come from ice loss in Antarctica, which is currently contributing less than 10 percent to global sea-level rise. Greenland will add another 25 percent to the total, while thermal expansion, currently the largest component of sea-level rise, will contribute only about 20 percent. The share from mountain glaciers will decline to less than 5 percent, mostly because many will shrink to a minimum.
“Continuous sea-level rise is something we cannot avoid unless global temperatures go down again,” Levermann says. “Thus we can be absolutely certain that we need to adapt.”
“Sea-level rise might be slow on the time scales on which we elect governments, but it is inevitable and therefore highly relevant for almost everything we build along our coastlines, for many generations to come.”
The International Energy Agency said last month that the world was on a path which was likely to result in a temperature increase of between 3.6 degrees Celsius and 5.3 degrees Celsius. The following week the World Bank said that, without concerted action now, the world could warm by two degrees Celsius within 20 or 30 years, and by 4 degrees Celsius by the end of the century.
Recent research suggests that even fairly modest sea-level rise is cause for concern, chiefly because of its ability to increase the probable frequency of severe storms and floods.
Earlier this month the World Meteorological Organization published its report, The Global Climate 2001-2010: A Decade of Climate Extremes.
It reported that during the decade from 2001 to 2010 “global mean sea levels rose about three millimeters (mm) per year, about double the observed 20th century trend of 1.6 mm per year. Global sea level averaged over the decade was about 20 centimeters higher than that of 1880.”
Visit EcoWatch’s CLIMATE CHANGE page for more related news on this topic.
At first glance, you wouldn't think avocados and almonds could harm bees; but a closer look at how these popular crops are produced reveals their potentially detrimental effect on pollinators.
Migratory beekeeping involves trucking millions of bees across the U.S. to pollinate different crops, including avocados and almonds. Timothy Paule II / Pexels / CC0<p>According to <a href="https://www.fromthegrapevine.com/israeli-kitchen/beekeeping-how-to-keep-bees" target="_blank">From the Grapevine</a>, American avocados also fully depend on bees' pollination to produce fruit, so farmers have turned to migratory beekeeping as well to fill the void left by wild populations.</p><p>U.S. farmers have become reliant upon the practice, but migratory beekeeping has been called exploitative and harmful to bees. <a href="https://www.cnn.com/2019/05/10/health/avocado-almond-vegan-partner/index.html" target="_blank">CNN</a> reported that commercial beekeeping may injure or kill bees and that transporting them to pollinate crops appears to negatively affect their health and lifespan. Because the honeybees are forced to gather pollen and nectar from a single, monoculture crop — the one they've been brought in to pollinate — they are deprived of their normal diet, which is more diverse and nourishing as it's comprised of a variety of pollens and nectars, Scientific American reported.</p><p>Scientific American added how getting shuttled from crop to crop and field to field across the country boomerangs the bees between feast and famine, especially once the blooms they were brought in to fertilize end.</p><p>Plus, the artificial mass influx of bees guarantees spreading viruses, mites and fungi between the insects as they collide in midair and crawl over each other in their hives, Scientific American reported. According to CNN, some researchers argue that this explains why so many bees die each winter, and even why entire hives suddenly die off in a phenomenon called colony collapse disorder.</p>
Avocado and almond crops depend on bees for proper pollination. FRANK MERIÑO / Pexels / CC0<p>Salazar and other Columbian beekeepers described "scooping up piles of dead bees" year after year since the avocado and citrus booms began, according to Phys.org. Many have opted to salvage what partial colonies survive and move away from agricultural areas.</p><p>The future of pollinators and the crops they help create is uncertain. According to the United Nations, nearly half of insect pollinators, particularly bees and butterflies, risk global extinction, Phys.org reported. Their decline already has cascading consequences for the economy and beyond. Roughly 1.4 billion jobs and three-quarters of all crops around the world depend on bees and other pollinators for free fertilization services worth billions of dollars, Phys.org noted. Losing wild and native bees could <a href="https://www.ecowatch.com/wild-bees-crop-shortage-2646849232.html" target="_self">trigger food security issues</a>.</p><p>Salazar, the beekeeper, warned Phys.org, "The bee is a bioindicator. If bees are dying, what other insects beneficial to the environment... are dying?"</p>
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