Lakes make a tiny fraction of the world's water, but they're home to lots of plants and animals. They're often situated in the midst of still more biodiversity, in the form of forest. At least, they used to be.
Lately, forests have been vanishing, while aquatic plants continue to thrive. Due to this change, the lakes of the Northern Hemisphere could almost double their methane emissions over the next 50 years, new research has shown. Why? Climate change.
This increase of emissions will further contribute to global warming, in what scientists call a positive climate feedback loop.
And it's just the latest addition to a growing list of ways we're altering natural processes with spiraling impacts on the climate and carbon cycle. Here are some of the most alarming:
More and more methane
Freshwater bodies are responsible for more than 15% of the Earth's natural emissions of methane, a greenhouse gas 25 times more potent than carbon dioxide.
Up to 77% of a lake's methane emissions come from the decomposition of aquatic plants. Microbes break down organic matter and generate methane that bubbles up to the surface.
Warming temperatures encourage the growth of aquatic plants, meaning there is more of this carbon-rich matter to break down, releasing still more climate-harmful methane into the atmosphere.
Researchers also found that debris from surrounding trees impedes methane production within the lake. But with fewer trees surrounding lakes that safety catch is also off.
A melting sun shield
The dazzling white of polar ice isn't just eye-catching, it also helps keep the planet cool, reflecting the sun's rays back to space.
As ice melts that reflective coating is lost, exposing darker bodies of water and land, which absorb more of the sun's heat, leading to greater warming and, in turn, to more ice melting... and so on.
This scary process is known as ice-albedo feedback.
Defrosting the permafrost
Permafrost is ground that has remained frozen for more than two consecutive years. It covers about 20% of the surface of the Earth — mostly in Canada, Russia and Alaska — and stores huge amounts of carbon, some of it for thousands or even millions of years.
As the planet warms up, permafrost is thawing. The IPCC estimates that permafrost in southern Alaska has become 4 millimeters thinner each year since 1992.
This thawing can put buildings and other infrastructure at risk, as a number of cities are built on permafrost. But it entails another and very worrying risk. Microbes in the newly defrosted soil become active, transforming once-frozen carbon into carbon dioxide and methane.
Scientists are very concerned about the impact of these greenhouse gases on the climate, but the true scale of the problem is still unknown.
Ring of fire
Forest fires have had devastating consequences in countries like Indonesia, California or Spain over the last few years. Alongside other human activity — like unsustainable land use — warmer temperatures and drier land due to climate change increase the risk and scale of forest fires.
Various studies found that large forest fires in the western United States have become five times more frequent since the 1970s and 80s, scorching over six times as much land, and lasting almost five times as long.
Burning all that wood and other organic matter, forest fires release massive amounts of carbon dioxide back into the atmosphere, helping push the global temperature and further dying out the land...
Cascading forest loss
Trees, of course, need water to survive. But they don't just consume this precious resource, they also help regulate it in the atmosphere. In the Amazon, the world's largest tropical rainforest, researchers are warning that a dangerous vicious circle might be taking place.
Rising temperatures close to the equator mean less rainfall, and even drought, which increases the risk of forest dieback. As drought takes its toll, there are fewer trees to absorb water and release it back, which in turns makes conditions still drier.
This "cascading dieback" is also worrying because forests are famously important carbon sinks, and forest loss a significant source of CO2 emissions.
Bonus track: Look down, soils matter
Soils hold 70% of the planet's land-based carbon — four times as much as all the world's biomass and three times the amount of CO2 in the atmosphere. Carbon could remain locked into the soil for millennia if we just left it alone. But unsustainable agriculture means it often escapes as carbon dioxide.
Since the start of the industrial revolution, a startling 50 to 70% of carbon once stored in soil has already been released into the atmosphere.
Loss of peatlands — which store huge amount of carbon — has a particularly terrifying impact, currently contributing 5% of global CO2 emissions and fueling forest fires.
While not a feedback loop, the example of CO2 from soils is a stark reminder of the delicate balance of our planetary system and the profound damage we do by upsetting it.