Video: Less Ice Means a Much Hotter Earth By 2100
By Roz Pidcock
The Arctic is intricately linked to Earth's climate. As Arctic sea ice declines, the effects are being felt far beyond the Arctic region. Now a new study shows how losing sea ice means the top of the planet is absorbing more heat than it did just three decades ago—and it makes for a sobering read.
Scientists have noticed big changes in the Arctic since satellites started observing earth from space, thirty years ago. The area covered by sea ice is getting smaller and the ice is getting thinner, due largely to rising global temperature.
The loss is most noticeable at the end of summer, when sea ice shrinks to a minimum, as part of its seasonal cycle. In September 2012, Arctic sea ice reached its lowest extent since satellite records began.
Knock On Effects
Losing sea ice has knock on effects for climate. One of the most direct consequences is that losing sea ice changes something scientists call albedo. Albedo is a measure of how well the earth's surface reflects sunlight.
Snow-covered sea ice has a high albedo, reflecting up to 85 percent of sunlight. As the area covered by ice and snow gets smaller, sunlight that would have been reflected is absorbed by open water instead, warming it up.
It's not only the ocean that warms. Heat from the warmer sea is released back into the air—raising atmospheric temperatures too. In turn, this melts more ice. It's largely for this reason that the Arctic region is warming twice as fast as the rest of the planet.
To find out how much Arctic ice loss is likely to influence and be influenced by warming in the coming century, scientists need a good understanding of how albedo has changed in response to recent temperature changes.
This is exactly what new research, published in Nature Climate Change, looks at. It examines how Arctic albedo has changed over almost three decades, between 1982 and 2009.
The team of scientists from Finland use new satellite measurements of reflectivity throughout the melt season, from May to August, to look for trends over time across the whole Arctic region.
Every month except May has seen a decline in sea ice albedo over the 28-year period, the research finds. The exception didn't come as a surprise, say the researchers. Other studies have shown thick snow cover in May means the albedo doesn't change much.
The most rapid drop in albedo is seen in the month of August, when snow and ice melt is highest. The data suggests a fall in albedo of about three per cent per decade over the study period.
The loss is pretty clear in the satellite images below, which show albedo for the month of August in 1985 on the left and in 2008 on the right. Marked in red, areas with an albedo of 75 percent or more have all but disappeared and have been replaced by green, which represents about 40 percent. There is quite a lot more light blue, up to 30 percent, and dark blue, which is 15 percent and under.
Albedo is also affected by changes in the condition of the ice that remains. For example, ice is getting darker as industrial soot—known as black carbon—is finding its way into the Arctic.
Data from other studies suggest the rate of Arctic ice melt has accelerated since the 1990s, which might imply the rate of albedo loss has accelerated too. The new paper looks at this possibility but concludes there is too much year-to-year variability in this short time frame to come to any firm conclusions.
While albedo loss is most pronounced in August, the paper points out the drop in early summer is most important for global temperature, as that's typically when solar output is at its highest.
A warming Arctic has implications for the neighboring Greenland ice sheet and Arctic wildlife—from the smallest algae to the biggest predators. On top of these more established impacts, scientists think sea ice loss might be disrupting winter weather in the northern hemisphere—another way that the impacts of change at the top of the planet might extend well beyond just the Arctic region.
Visit EcoWatch’s CLIMATE CHANGE page for more related news on this topic.
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A Game of Jenga<p>Think of it as a game of Jenga and the planet's climate system as the tower. For generations, we have been slowly removing blocks. But at some point, we will remove a pivotal block, such as the collapse of one of the major global ocean circulation systems, for example the Atlantic Meridional Overturning Circulation (AMOC), that will cause all or part of the global climate system to fall into a planetary emergency.</p><p>But worse still, it could cause runaway damage: Where the tipping points form a domino-like cascade, where breaching one triggers breaches of others, creating an unstoppable shift to a radically and swiftly changing climate.</p><p>One of the most concerning tipping points is mass methane release. Methane can be found in deep freeze storage within permafrost and at the bottom of the deepest oceans in the form of methane hydrates. But rising sea and air temperatures are beginning to thaw these stores of methane.</p><p>This would release a powerful greenhouse gas into the atmosphere, 30-times more potent than carbon dioxide as a global warming agent. This would drastically increase temperatures and rush us towards the breach of other tipping points.</p><p>This could include the acceleration of ice thaw on all three of the globe's large, land-based ice sheets – Greenland, West Antarctica and the Wilkes Basin in East Antarctica. The potential collapse of the West Antarctic ice sheet is seen as a key tipping point, as its loss could eventually <a href="https://science.sciencemag.org/content/324/5929/901" target="_blank">raise global sea levels by 3.3 meters</a> with important regional variations.</p><p>More than that, we would be on the irreversible path to full land-ice melt, causing sea levels to rise by up to 30 meters, roughly at the rate of two meters per century, or maybe faster. Just look at the raised beaches around the world, at the last high stand of global sea level, at the end of the Pleistocene period around 120,0000 years ago, to see the evidence of such a warm world, which was just 2°C warmer than the present day.</p>
Cutting Off Circulation<p>As well as devastating low-lying and coastal areas around the world, melting polar ice could set off another tipping point: a disablement to the AMOC.</p><p>This circulation system drives a northward flow of warm, salty water on the upper layers of the ocean from the tropics to the northeast Atlantic region, and a southward flow of cold water deep in the ocean.</p><p>The ocean conveyor belt has a major effect on the climate, seasonal cycles and temperature in western and northern Europe. It means the region is warmer than other areas of similar latitude.</p><p>But melting ice from the Greenland ice sheet could threaten the AMOC system. It would dilute the salty sea water in the north Atlantic, making the water lighter and less able or unable to sink. This would slow the engine that drives this ocean circulation.</p><p><a href="https://www.carbonbrief.org/atlantic-conveyor-belt-has-slowed-15-per-cent-since-mid-twentieth-century" target="_blank">Recent research</a> suggests the AMOC has already weakened by around 15% since the middle of the 20th century. If this continues, it could have a major impact on the climate of the northern hemisphere, but particularly Europe. It may even lead to the <a href="https://ore.exeter.ac.uk/repository/handle/10871/39731?show=full" target="_blank" rel="noopener noreferrer">cessation of arable farming</a> in the UK, for instance.</p><p>It may also reduce rainfall over the Amazon basin, impact the monsoon systems in Asia and, by bringing warm waters into the Southern Ocean, further destabilize ice in Antarctica and accelerate global sea level rise.</p>
The Atlantic Meridional Overturning Circulation has a major effect on the climate. Praetorius (2018)
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