A day before the U.N. Climate Action Summit, leading climate science organizations said on Sunday that nations must reduce "glaring and growing gaps" between what they will do and what they must do to fight global warming.
Their 28-page report, called "United in Science," concluded that countries will have to triple their carbon emissions-cutting targets to fulfill the 2015 Paris Agreement’s minimum goal of preventing average global temperatures from rising more than 2 degrees Celsius above pre-industrial levels.
It said that nations' current plans for reducing emissions of carbon dioxide, methane and other heat-trapping greenhouse gases would lead to a rise in average global temperatures of between 2.9 degrees C. and 3.4 degrees C. by the end of the 21st century, with catastrophic results for the natural world and humankind.
U.N. Secretary-General António Guterres had told the leaders of the G-20 major economies at a summit in Osaka, Japan last June that he was convening a Climate Action Summit because "to make sure that we are able to abide by what the scientific community is telling us is absolutely essential to rescue the planet.”
The synthesis report of up-to-date climate science findings was prepared by three U.N. agencies — the World Meteorological Organization, or WMO; the Intergovernmental Panel on Climate Change, or IPCC; and U.N. Environment — along with Earth League, Future Earth, Global Carbon Project and The Energy and Resources Institute of India, or TERI.
"This is a very important first step in politics: acknowledging and welcoming the compelling information," said Andrés Couve, Chile’s new minister of science, technology and innovation, whose country will host the next major U.N.-hosted round of global climate negotiations in December.
"Second, we realize that fear, with catastrophic and apocalyptic scenarios, only serves to paralyze us," he said. "Time for action also means embracing a responsible, solutions perspective."
Since the world has already warmed by 1 degree C. since the Industrial Revolution, the Paris accord's goal requires keeping the planet from heating on average by no more than another 1 degree C. The Paris accord, however, also calls for limiting the warming to 1.5 degrees C. above pre-industrial levels, if possible — which would be just a half-degree C. more than current levels.
The report concluded that nations will have to increase their emissions-cutting ambitions five-fold to keep global warming to no more than a half-degree C. more. That was among the demands of the more than 4 million people who turned out for global climate strikes on Friday. They urged world leaders to do everything they can to limit global warming, ensure climate justice and equity and listen to the best science available.
Earlier in the week, 16-year-old Swedish climate activist Greta Thunberg testified before two committees in the U.S. Congress and demanded that its members “listen to the scientists” about the threat of a warming planet.
Thunberg attached the major report that the Nobel-prize winning IPCC released last October as her testimony, rather than deliver her own speech. The report said even the most optimistic scenarios for action under the Paris accord will result in serious repercussions for the world and future generations.
It said that a half-degree C. less warming would cause fewer deaths and illnesses, and 0.1 meters less sea rise, and it would halve the number of people who lacked fresh water. Substantially fewer heatwaves and droughts would result, it said, and the world’s coral reefs might survive.
Limiting the global average temperature increase to 1.5 degrees C. would avert 150 million premature deaths over the 21st century, it said, but the global economy must become “carbon neutral” by 2050 and start forcing a sharply downward curve in carbon dioxide emissions to the atmosphere starting in 2020.
“I am submitting this report as my testimony because I don’t want you to listen to me, I want you to listen to the scientists,” Thunberg told members of Congress. “I want you to unite behind science. And then I want you to take real action.”
A unified assessment
As the Earth grapples with anthropogenic climate change, world leaders need the best available science to develop "concrete actions that halt global warming and the worst effects of climate change,” said the U.N.'s Science Advisory Group that produced the report.
"Limiting warming to 1.5 degrees C. is not physically impossible but would require unprecedented transitions in all aspects of society," the group advised. "There are clear benefits to keeping warming to 1.5 degrees C. compared to 2 degrees C. or higher. Every bit of warming matters."
The group was co-chaired by Petteri Taalas, WMO's secretary-general, and Leena Srivastava, outgoing vice chancellor of the TERI School of Advanced Studies. Each of the contributing organizations provided short summaries for the report, which was coordinated by WMO.
“Our ambitions to reverse the global climate emergency are backed by solid science and data," said Inger Andersen, UNEP's executive director. "What we need more than ever is to see bold policy action and further investment and research into cleaner, greener energy. This will ensure we are able to roll back emissions."
The report found:
—The average global temperature for 2015 to 2019 is on track to be the warmest of any equivalent period on record and estimated to be 1.1° C. above pre-industrial times from 1850 to 1900.
—Arctic summer sea-ice extent declined at a rate of approximately 12% per decade between 1979 and 2018. The four lowest values for winter sea-ice extent occurred between 2015 and 2019. Overall, the amount of ice lost annually from the Antarctic ice sheet increased at least six-fold between 1979 and 2017. Glacier mass loss for 2015 to 2019 is the highest for any five-year period on record.
—The observed rate of global mean sea-level rise accelerated from 3.04 millimeters per year between 1997 and 2006 up to approximately 4mm per year between 2007 and 2016. This resulted from faster ocean warming and melting of the Greenland and West Antarctica ice sheets. Ocean acidity increased by 26% overall since the start of the industrial era.
—Levels of the main long-lived greenhouse gases — carbon dioxide, methane and nitrous oxide — reached new highs. The last time Earth’s atmosphere contained 400 parts per million of CO2 was about 3 million to 5 million years ago, when global mean surface temperatures were 2 degrees to 3 degrees C. warmer than today.
—In 2018, global CO2 concentration was 407.8 ppm, or 2.2 ppm higher than 2017. Preliminary data indicate that CO2 concentrations are on track to reach or exceed 410 ppm by the end of 2019.
—Carbon dioxide emissions grew 2% and reached a record high of 37 billion tons in 2018. There is still no sign of a peak in global emissions, even though they are growing slower than the global economy.
—Current economic and energy trends suggest emissions will be at least as high in 2019 as in 2018. Global GDP is expected to grow 3.2% in 2019, and if the global economy decarbonized at the same rate as in the last 10 years, that would still lead to an increase in global emissions. Global greenhouse gas emissions are not estimated to peak by 2030, let alone by 2020.
—Natural CO2 sinks, such as vegetation and oceans, remove about half of all emissions from human activities, but are becoming less efficient, emphasizing the need to reduce deforestation and expand natural CO2 sinks, particularly those in forests and soils that can be improved by better management and habitat restoration.