If humans pump enough carbon dioxide (CO₂) into the atmosphere, the stratocumulus clouds(层积云 ) could disappear, and the earth's temperature could climb sharply to heights not predicted in current climate models. It would burn the planet. That's the conclusion of a paper published in the journal Nature Geoscience and described in detail by Natalie Wolchover for Quanta Magazine.

As Wolchover explained, clouds have long been one of the great uncertainties of climate models. Computer models that easily capture the complexity and detail of most climate systems just aren't powerful enough to predict worldwide changes in cloud behavior. But clouds are important. They reflect sunlight away from the earth's surface. And stratocumulus clouds are those white blankets you might have seen as you looked out the window of arm airplane, rolling out below you and hiding the ground Researchers suspect that certain sudden, past jumps in temperature may have been caused by changes to clouds like these.

For the new research, scientists modeled just a small patch of sky using a supercomputer. They found that if carbon dioxide levels reach about 1, 200 parts per million(ppm) in the atmosphere, stratocumulus clouds break up. That's a very high carbon dioxide concentration.   Right now, levels have climbed past 410 ppm--a dangerous change from 280 ppm before the Industrial Revolution.

But humans put more and more CO₂ into the atmosphere every year. If current trends continue, the earth could reach 1, 200 ppm within 100 to 150 years. This could happen if our society doesn't follow through on any of its commitments to reduce emissions(排放), Wolchover reported. And even if it does, the result would be another 8 degrees Celsius of heat added to the global average, on top of the dangerous changes already underway due to greenhouse gases.

That’s an enormous change, and it goes beyond predictions of worldwide ice melt and catastrophic sea level rise. And, once the stratocumulus clouds are gone, Wolchover reported, they likely wouldn't reappear until atmospheric carbon dioxide levels dropped below where they are currently.

There's still some uncertainty in the data. The 1, 200 ppm figure could change as scientists look into the issue further.

In recent years some extreme weather events have arisen from global warming because of human activities, with studies indicating an increasing threat from extreme weather in the future. Scientists were certain that global warming is being caused mostly by increasing concentrations of greenhouse gases and other human activities.

Its effects include warming global temperature rising sea levels and expansion of deserts in the subtropics (亚热带). Warming is expected to be greater over land than over the oceans and greatest in the Arctic, with the continuing loss of glaciers, permafrost and sea ice. Other likely changes include more frequent extreme weather events including heat waves, droughts, heavy rainfall with floods, heavy snow-fall and species extinction due to great change of temperature. Bad effects on humans include the threat to food security from decreasing crop yields and the loss of populated (住人的) areas because of rising sea levels.

Possible responses to global warming are reduction of emissions (排放), adaptation to its effects, building systems resilient to its effects, and possible future climate engineering Most countries are parties to the United Nations Framework Convention on Climate Change (UNFCCC), whose objective is to prevent dangerous climate change. It has adopted a range of policies designed to reduce greenhouse gas and to assist in adaptation to global warming. It is agreed that future global warming should be limited to below 2.0℃ (3.6°F) relative to the pre-industrial level.

On 12 November 2019, NASA scientists reported that human-made carbon dioxide continues to increase above levels that have not been seen in hundreds of thousands of years: currently, about half of the carbon dioxide released from the burning of fossil fuels remains in the atmosphere and is not absorbed by vegetation and the oceans.

For millions of years, Arctic sea ice has expanded and shrunk in a rhythmic dance with the summer sun. Humans evolved in this icy world, and civilization relied on it for climatic, ecological and political stability. But now the world comes ever closer to a future without ice. The National Snow and Ice Data Center reported that 2019’s minimum arctic sea ice extent was the second lowest on record. Arctic summers could become mostly ice-free in 30 years, and possibly sooner if current trends continue. As the northern sea ice declines, the world must unite to preserve what remains of the Arctic.

Although most people have never seen the sea ice, its effects are never far away. By reflecting sunlight, Arctic ice acts as Earth’s air conditioner. Once dark water replaces brilliant ice, Earth could warm substantially, equivalent to the warming caused by the additional release of a trillion tons of carbon dioxide (CO₂) into the atmosphere and declining sea ice threatens wildlife, from the polar bear to algae that grow beneath the sea ice, supporting the large amount of marine life.

To avoid the consequences the scientific community should advocate not just for lowering greenhouse gas emissions, but also for protecting the Arctic from exploitation. The Antarctic shows the way. In the 1950s, countries raced to claim the Antarctic continent for resources and military installations. Enter the scientists. The 1957-1958 International Geophysical Year brought together scientists from competing countries to study Antarctica, and countries temporarily suspended their territorial disputes (争议). In 1959, 12 countries signed the Antarctic Treaty to preserve the continent for peaceful scientific discovery rather than territorial and military gain.

Sixty years later, we must now save the Arctic. A new Marine Arctic Peace Sanctuary (MAPS) Treaty would protect the Arctic Ocean as a scientific preserve for peaceful purposes only. Similar to Antarctica, MAPS would prohibit resource exploitation, commercial fishing and shipping, and military exercises. So far, only 2 non-Arctic countries have signed MAPS; 97 more need to sign on to enact it into law. Scientists can help—just as they did for the Antarctic—by giving statements of support, asking scientific organizations to endorse (支持) the treaty, communicating the importance of protecting the arctic to the public and policy-makers, and above all, by convincing national leaders to sign the treaty. In particular, Arctic nations must agree that recognizing the arctic as an international preserve is better than fighting over it. In 2018, these countries successfully negotiated a 16-year moratorium on commercial fishing in the Arctic high seas, demonstrating that such agreements are possible.

Humans have only ever lived in a world topped by ice. Can we now work together to protect Arctic ecosystems, keep the northern peace, and allow the sea ice to return?