Illustration by Mia Clement – sketch of an ice sheet
The ocean plays a central role in regulating the Earth’s climate. The Fifth Assessment Report published by the Intergovernmental Panel on Climate Change (IPCC) in 2013 revealed that it has thus far absorbed 93% of the extra energy from the enhanced greenhouse effect, with warming now being observed at depths of 1,000 m. As a consequence, this has led to increased ocean stratification (prevention of water mixing due to different properties of water masses), changes in ocean current regimes, and expansion of depleted oxygen zones. Changes in the geographical ranges of marine species and shifts in growing seasons, as well as in the diversity and abundance of species communities are now being observed. At the same time, weather patterns are changing, with extreme events increasing in frequency.
Much like the ocean, the cryosphere is integral for climate regulation. Ice and snow on land are one part of the cryosphere. This includes the largest parts of the cryosphere, the continental ice sheets found in Greenland and Antarctica, as well as ice caps, glaciers, and areas of snow and permafrost. When continental ice flows out from land and to the sea surface, we get shelf ice. The other part of the cryosphere is ice that is found in water. This includes frozen parts of the ocean, such as waters surrounding Antarctica and the Arctic. It also includes frozen rivers and lakes, which mainly occur in polar areas.
The components of the cryosphere play an important role in the Earth’s climate. Snow and ice reflect heat from the sun, helping to regulate our planet’s temperature. Because polar regions are some of the most sensitive to climate shifts, the cryosphere may be one of the first places where scientists are able to identify global changes in climate. This piece explores the changes in the ocean and the cryosphere using the Gulf Stream and permafrost regions as key studies.
Changes in the ocean
A new study suggests that the Gulf Stream, one of Earth’s major climate-regulating ocean currents, is moving slower than it has in thousands of years. Human-induced climate change is primarily to blame. The researchers found that this “unprecedented” slowdown could impact weather patterns and sea levels on both sides of the Atlantic. And it only looks poised to worsen over the coming decades if climate change continues unabated. Indeed, suppose global warming persists at its current pace. In that case, the Gulf Stream could pass a critical “tipping point” by the year 2100, potentially causing the current to grind to a halt, regardless of the climate, said lead study author Levke Caesar, a climatologist at Maynooth University in Ireland..
This disruption could unleash rising sea levels along the coasts of North America and northwestern Europe and usher in more extreme weather such as heatwaves and cyclones.
“The signs of destabilisation being visible already is something that I wouldn’t have expected and that I find scary”
Niklas Boers, from the Potsdam Institute for Climate Impact Research in Germany.
The Gulf Stream (also known as the Atlantic Meridional Overturning Circulation, or AMOC) is essentially a “giant conveyor belt” along the East coast of the United States, study co-author Stefan Rahmstorf, a researcher at the Potsdam Institute for Climate Impact Research (PIK) in Germany, said to Phys.org.
The current begins near the Florida Peninsula, carrying warm surface water north toward Newfoundland before meandering east across the Atlantic. By the time it reaches the North Atlantic, that warm surface water becomes cooler, saltier and denser, sinking into the deep sea before being driven south again, where the cycle repeats. According to Rahmstorf, the current moves more than 5.2 billion gallons (20 million cubic meters) of water per second, or “almost 100 times the Amazon [River] flow.”
(Image credit: RedAndr/ NOAA/ CC 4.0)
This wet conveyor belt has myriad climate impacts on both sides of the Atlantic, keeping temperatures in Florida and the U.K. mild, influencing the path and strength of cyclones and helping to regulate sea levels. However, since direct measurements began in 2004, scientists have detected a troubling pattern: AMOC currents are getting slower and weaker.
“These signs of decreasing stability are concerning. But we still don’t know if a collapse will occur or how close we might be to it.”
David Thornalley, at University College London in the UK, whose work showed the AMOC is at its weakest point in 1,600 years
Global warming increases annual rainfall and accelerates the melting of ice sheets, including the Greenland Ice Sheet in the North Atlantic. These factors dump ever greater amounts of fresh water into the ocean, reducing the density and salinity of the surface water at the northern end of the Gulf Stream conveyor belt. According to the researchers, this freshwater inhibits how quickly the water can sink and begin its journey back south, weakening the overall flow of the AMOC.
Changes to perma-frost cover
Archaeological finds buried deep in Siberian permafrost have turned up with increasing regularity. Just days ago, two well-preserved bodies of the long-extinct cave lion were uncovered in Russia’s Yakutia region. The older cadaver is now ascertained to have lived over 43,000 years ago. Climate change is warming the Arctic faster than the rest of the world and has thawed some areas of permafrost deeply enough to encover artefacts locked in ice for tens of thousands of years.
Permafrost occupies about 25% of the Northern Hemisphere’s terrestrial surface and almost 65% of Russia’s. Things are not looking good for Russia’s permafrost, which is experiencing some of the highest rates of thawing worldwide.
Changes in permafrost have important implications for natural systems, humans, and the economy of the northern lands. Results from mathematical modelling indicate that by the mid-21st century, near-surface permafrost in the Northern Hemisphere may shrink by 15%-30%, leading to complete thawing of the frozen ground in the upper few meters. In contrast, elsewhere, the depth of seasonal thawing may increase on average by 15%-25% and by 50% or more in the northernmost locations.
Image credit to: https://eos.org/science-updates/is-the-northern-permafrost-zone-a-source-or-a-sink-for-carbon
Such changes may shift the balance between the uptake and release of carbon in the tundra and facilitate the emission of greenhouse gases from the carbon-rich Arctic wetlands. Serious public concerns are associated with the effects that thawing permafrost may have on its infrastructure. Degradation of permafrost and ground settlement due to thermokarst may lead to dramatic distortions of terrain and changes in hydrology and vegetation. Thermokarst features are topographic depressions formed as a result of thawing ground ice, present in areas where the thermal equilibrium has shifted, allowing for the thaw of ground ice. This process can be a result of lateral erosion where ground ice becomes exposed or lateral degradation where warm surface water penetrates into the adjacent shore, causing ground ice to thaw. It may lead ultimately to the transformation of existing landforms. Recent studies indicate that non-climatic factors, such as changes in vegetation and hydrology, may largely govern the response of permafrost to global warming. More studies are needed to understand better and quantify the effects of multiple factors in the changing northern environment.
“If the methane released during gas hydrate degradation reaches the ocean, it would mostly be consumed by bacteria in the water column and not reach the atmosphere. Degrading gas hydrate is usually deeply buried in permafrost areas, so permafrost thaw is the more [sic] important contributor to greenhouse gas emissions.”
Dr Carolyn Ruppel’s, chief scientist for the US Geological Survey’s Gas Hydrates Project, statement to Carbon Brief.
In high-latitude regions of the Earth, temperatures have risen 0.6 °C per decade, twice as fast as the global average. Ground temperatures can rise even more quickly. Mean yearly ground temperatures rose from 0.03 to 0.06 °C per year at 10–12 m in the continuous permafrost zone. The permafrost table at all sites has lowered up to 8 m in the discontinuous permafrost zone. The resulting thaw of frozen ground exposes substantial quantities of organic carbon to decomposition by soil microbes. The permafrost region contains twice as much carbon as there is currently in the atmosphere. A considerable fraction of this material can be mineralised by microbes and converted to CO2 and CH4 on timescales of years to decades. At the proposed rates, the observed and projected emissions of CH4 and CO2 from thawing permafrost are unlikely to cause abrupt climate change over a few years to a decade. Instead, permafrost carbon emissions are likely to be felt over decades to centuries as northern regions warm, making climate change happen faster than we would expect based on projected emissions from human activities alone.
Another potential feedback of thawing permafrost relates to changes in vegetation distribution. Shrubs and boreal forests may extend northward, resulting in further positive climate feedback due to lower albedos over shrubs and forests than tundra grasses and moss.
Permafrost degradation impacts Arctic hydrology and results in slow soil drying and redistribution of runoff into sub-surface runoff at the expense of surface runoff. Over the past 70 years, runoff to the Arctic Ocean has increased by an estimated 7%. Change in the amount of fresh water reaching the Arctic Ocean affects sea-ice formation and may alter the oceanic thermohaline circulation. Model results indicate that discharge grows by 28% by 2100, primarily due to increases in precipitation that exceed increases in evaporation. However, 15% of the growth is attributed to contributions from thawing permafrost.
Conclusion
Both the changes in the Gulf Stream and permafrost regions are two case studies in an ever-growing field of ‘climate changed’ landscapes and spaces. With changes in thermal gradients in oceanic currents and increased temperatures resulting in the thawing of fundamental regions of permafrost, humanity is drawing ever closer to the edge of environmental devastation. The effects of climate change are likely to be some of the biggest environmental challenges our generation has ever faced. This climate crisis is only just starting.