A joint study by international climate scientists from Germany, Sweden, Denmark and Australia presents a bleak prognosis: Even if the goals of the Paris climate agreement are achieved and global warming is limited to maxiumum 2 degrees Celsius (3.6 degrees Fahrenheit) compared to pre-industrial levels, the climate system could still pass a devastating tipping point.

"Human emissions of greenhouse gas are not the sole determinant of temperature on Earth," said Will Steffen, lead author of the study and climate researcher at the Australian National University and the Swedish research institute Stockholm Resilience Centre.

"Our study suggests that human-induced global warming of 2 degrees Celsius may trigger other Earth system processes, often called 'feedbacks,' that can drive further warming — even if we stop emitting greenhouse gases," he said.

The global average temperature in such a case would in the long term settle between 4 to 5 degrees warmer compared to pre-industrial levels, their study found.

Sea levels would rise 10 to 60 meters (33 to 197 feet), flooding numerous islands and coastal cities such as Venice, New York, Tokyo and Sydney. Such major population centers would have to be abandoned.

Scientists call this a "hothouse Earth" climate scenario.

Read more: The global heat wave that's been killing us

The heat wave goes on ... and on Portugal: Sitting is good ... This man in the Portuguese capital, Lisbon, seems to be enjoying the feeling of sun on his face. And Portugal has been having plenty of it, as the Iberian Peninsula bakes in warmth coming over from North Africa. The country has already had near-record temperatures this year, but nothing yet to break the 47.3° C (117.1° F) recorded in 2003 in Amareleja. Still, large parts are on red alert.

The heat wave goes on ... and on ... but being near water is better Fountains, like this one in Rossio Square in Lisbon, provide welcome relief from the heat. Portugal is not just experiencing a heat wave, but also clouds of dust coming from the Sahara Desert that are tingeing the sky dark yellow in some places.

The heat wave goes on ... and on Spain: Also taking the brunt In neighboring Spain, the mercury is also soaring and heat warnings have been issued. Three people are reported to have died from heat-related causes in the past week. Authorities are warning people to shelter from the sun and drink plenty of fluids, advice heeded by this man in Madrid.

The heat wave goes on ... and on Germany: Low rainfall and burning sun Despite its northerly location in Europe, much of Germany has been experiencing an unusually long run of high temperatures, accompanied by much less rainfall than usual. Farmers have requested financial aid from the government to help them cope with greatly reduced harvests.

The heat wave goes on ... and on A desert landscape? The heat in Germany has caused the waters in the Rhine River to drop dramatically leaving parts of the riverbed dry, as seen here in Düsseldorf. Freight vessels are being forced to reduce their cargoes if they want to continue sailing on the river.

The heat wave goes on ... and on Austria: Paw protection In the Austrian capital, Vienna, asphalt in the city has become too hot for police dogs' paws, so the force has come up with the logical response: specially made dog shoes. The working dog shown here, Spike, seems as alert as ever and completely unfazed by his new item of uniform.

The heat wave goes on ... and on Sweden: Taking advantage Sweden has had its hottest July of the past 260 years. The high temperatures have led to a high fire danger, and wildfires in the country have extended even into the Arctic Circle. But these city dwellers in central Stockholm seem intent on seeing the bright side of the hot weather as they laze at the Tantolunden bathing place.

The heat wave goes on ... and on Britain: Brown and yellow everywhere In Britain, the unusually long summer has taken its toll on lawns and plants across the country. Fire authorities have warned that parks and other grasslands are like a tinderbox after a July that was the country's third-warmest month in more than a century. Greenwich Park in London, seen here, seems to be no exception.

The heat wave goes on ... and on Looking cool But relief can been found even in central London, as seen here in a fountain at Trafalgar Square. Retailers are also suffering, groaning not just about the heat but also over decreased sales: Accountancy firm BDO said figures were down 1.1 percent in July. "The scorching conditions did not encourage physical shopping and only hindered footfall in shops," BDO's Sophie Michael said.

The heat wave goes on ... and on North Korea: 'Natural disaster' North Korea has called for an "all-out battle" against record temperatures, with crops damaged amid the prolonged heat wave. Poor harvests could hit hard in a country that is already struggling under international sanctions over its nuclear arms program. North Korea also lacks irrigation systems and other infrastructure to cope with drought.

The heat wave goes on ... and on The simple fan: A boon for all These men in Pyongyang transporting an electric fan have obviously adopted one of the cheapest, yet most effective, ways of countering heat: the humble electric fan. They seem not to believe a widespread South Korean myth: that fans can cause death if left on while someone is asleep. The fact is, of course, that people are much more likely to die from the heat without one running. Author: Timothy Jones



Climate domino effect

In the study published Monday in the Proceedings of the National Academy of Sciences (PNAS), the international research team analyzed the complete climate system of a 2-degree warmer world across several models.

Interactions and chain reactions among melting glaciers, thawing permafrost, bacteria in the oceans and weakened carbon sinks were discovered.

Read more: When nature harms itself — five scary climate feedback loops

As a result of these feedback processes and tipping points that lead to abrupt changes in the climate system, forests and permafrost transform themselves from "friends" that store CO2 and other greenhouse gases like methane into "enemies" that uncontrollably release stored emissions into the atmosphere.

As such, the individual feedback processes could potentially snowball, explained Johan Rockström, executive director of the Stockholm Resilience Centre and incoming co-director of the Potsdam Institute for Climate Impact Research (PIK).

Extreme weather is one consequence of climate change that is becoming ever more palpable

"These tipping elements can potentially act like a row of dominos. Once one is pushed over, it pushes Earth toward another. It may be very difficult or impossible to stop the whole row of dominoes from tumbling over," he said.

The Earth would then warm at an accelerating tempo — even if humans stopped producing greenhouse gases entirely.

"Places on Earth will become uninhabitable if 'hothouse Earth' becomes the reality," Rockström added.

Read more: Current heat waves are linked to climate change, scientists confirm

Minimizing 'self-amplifying' change

While the 2015 Paris Agreement, agreed to by 197 nations, settled on a 2-degree target, it is unclear whether this is enough to avert a climate catastrophe, warned Hans Joachim Schellnhuber, director of PIK and co-author of the study.

"We still do not know if the climate system can be safely 'parked' at 2 degrees," he said.

That is in no way to say that the Paris climate agreement is futile and should be abandoned — as United States President Donald Trump did in June 2017 when he pulled the world's second-largest greenhouse gas emitter out of the deal.

Trump referred to a tiny temperature increase when he announced US withdrawal from the landmark Paris climate agreement

"Fully implementing the Paris climate agreement by following a path of rapid decarbonization through socio-economic transformation minimizes the risk of triggering self-amplifying climate change," Jonathan Donges, a PIK researcher and co-author of the study, told DW.

He said that meeting the Paris goals — or even better, aiming for a more ambitious target — remains "the best-known strategy to minimize the risk of triggering self-reinforcing feedbacks in the Earth system that could lead to a hothouse climate state."

To avoid a potential chain reaction, much more needs to be done than just reducing greenhouse gas emissions, the researchers point out.

Humanity must protect the ecosystem as a whole; create more natural carbon sinks; stop deforestation; consume less; control population growth; invest in technologies that extract CO2 from the atmosphere; and much more. For Donges, such "stewardship" of the Earth will also require "transformed social values."

Read more: Earth Overshoot Day: Time for a radical rethink

'Positive message'

Despite the study's apocalyptic findings, co-author Katherine Richardson of the University of Copenhagen said they are not trying to present a hopeless doomsday scenario.

"I think our study has an incredible positive message," she told DW, adding that real action on climate change requires increased awareness of its potential effects.

"What we are really doing is understanding ever better our role in the Earth's system, and acting accordingly," Richardson added. "We would be screwed if we didn't recognize the fact that we are just not doing enough."