Heatwaves, rising seas, forest fires - scientists have been meeting in a sweltering Paris to discuss the latest thinking on managing climate change and avoiding its worst impacts, ahead of the key UN climate conference.
"We need to turn around the tide of rising emissions within the next few years, by the latest 2020, so that we actually stay below 2 degrees Celsius [3.6 degrees Fahrenheit] of global warming," climate expert Stefan Rahmstorf told DW from this week's Paris science event.
Ocean physicist Rahmstorf, one of the world's top climate experts, called this "stocktaking of the state of science" a key event. Taking place just a few months before COP21 - the UN climate conference that is charged with formalizing a new world climate agreement to succeed the Kyoto Protocol from 2020 onward - Rahmstorf said almost every speaker stressed the urgency of adopting substantial measures to reduce the world's output of greenhouse gases.
Climate change well underway
Almost 2,000 international scientists from a wide range of disciplines came to Paris to debate "Our Common Future Under Climate Change." The event was organized by the International Council for Science, Future Earth, UNESCO and major French research institutions, with support from the French government.
There was widespread consensus amongst the experts gathered in Paris that climate change impacts are already making themselves felt, and that more ambitious action to reduce greenhouse gas emissions is urgently needed.
According to the Intergovernmental Panel on Climate Change (IPCC), land and ocean surface temperatures have increased globally by nearly 1 degree Celsius since 1901. In parts of Africa, Asia, North America and South America, surface temperatures have risen by up to 2.5 degrees Celsius.
At the United Nations climate talks in 2010, governments committed to a maximum temperature rise of 2 degrees above pre-industrial levels. Climate expert Rahmstorf says that benchmark marks "a real danger level, where global warming may well become unmanageable and the risks are simply getting too high."
The latest analyses suggest even a 2-degree rise would involve a high risk of serious irreversible impacts, and that 1.5 degrees Celsius would be a more suitable upper limit.
However, the IPCC has also said that the Earth is actually heading toward average global warming of 5 to 6 degrees - unless greenhouse gas emissions are drastically reduced in the very near future.
Countries have been asked to submit their Intended Nationally Determined Contributions (INDCs) to the new climate agreement well ahead of COP21 in December. This refers to emission reductions pledges the countries intend to make.
Representing slightly more than half of global emissions, around 40 developed and developing nations have already submitted their pledges. In November, the UN Climate Secretariat will release a report on the aggregate INDC submissions. However, it is already clear that current pledges will not be sufficient to remain under the 2-degree target.
UN Secretary General Ban Ki-moon stated in a message to the participants of this week's Paris meeting:
"The emissions gap - the difference between emissions reductions pledged by parties to the UNFCCC and what is needed to stay within two degrees Celsius - has been increasing. So, too, has the adaptation gap - the difference between funding and capacity needed and what has been committed. To bridge these gaps, it is critical to fill holes in funding, knowledge, technology, capacity and trust."
Economic growth with zero emissions?
According to figures presented at the Paris meeting by scientists from the Laboratoire des Sciences du Climat et de l'Environnement, the top four emitters in 2013 accounted for 58 percent of global emissions: China (28 percent), United States (14 percent), the EU (28 member states taken together - 10 percent) and India (7 percent).
Substantial and sustained reductions would be essential to keep warming below 2 degrees. Scientists at the meeting said emissions of heat-trapping gases would have to be cut by 40 to 70 percent below current levels by 2050.
The key would be to decouple economic growth from carbon emissions. Continued trends based on IMF projections of economic growth suggest that by 2019, China's emissions could exceed those of the US, EU and India combined - and India could emit more than the EU.
At present emission rates, the remaining "carbon budget" - the maximum amount possible to still emit without crossing the 2-degree threshold - would be used up in about 30 years.
The IPCC reports stress that further warming will increase the likelihood of severe, pervasive and irreversible impacts for people and ecosystems. Such risks are unevenly distributed and are generally greater for disadvantaged people and communities.
Six-meter sea level rise?
The Paris stocktaking included recent scientific findings that were not available when the latest IPCC report was published two years ago. Rahmstorf mentions new documenting of irreversible melting in parts of the West Antarctic ice sheet, which will contribute to rising sea levels.
"Basically the message is: the kind of climate we are moving toward now - even if we limit warming to two degrees - has in the past always been associated with a several-meter-higher sea level," Rahmstorf told DW.
"This would of course have catastrophic consequences for many coastal cities and small island nations."
Solutions are possible
Experts in Paris were not looking only at the state of natural science, but also at ways of minimizing future climate change and its impacts.
Chris Field, head of the US Carnegie Institution's Department of Global Ecology, emphasized a wide variety of evidence-based solutions, which would be economically attractive and could be scaled up.
Rahmstorf told DW he feels more optimistic than he did a few years ago.
"The development of renewable energies - wind, solar and others - has really surpassed the most optimistic expectations," he said. "And so there is hope that if we really put our will to it, we will be able to stop global warming below 2 degrees, and hopefully closer to 1.5 degrees."
Hervé Le Treu, chair of the organizing committee and a professor of climatology at the Paris Université Pierre et Marie Curie, said the expertise showcased how scientists are engaged and collaborating more than ever in advancing solutions, especially for less-developed countries.
With extreme weather events on the increase around the globe - in line with what the IPCC experts predicted would happen as the planet warms - awareness of the need for rapid action to cut emissions could be on the rise.
Rahmstorf hopes people are recognizing that climate change is having a negative impact. "Climate protection is not about some nature protection issue - it is about protecting people from the massive risks we are facing if the climate changes further."