The newest climate report from the Intergovernmental Panel on Climate Change (IPCC) says that climate change is "unequivocally" caused by humans and warns that global temperatures are expected to reach a significant warming milestone in the next 20 years.
The planet is expected to reach average temperatures that are 1.5 degrees warmer than a pre-industrial baseline by 2040, according to the report, which was released on Monday.
A prior special report from the IPCC found that keeping warming below this level would prevent climate-related impacts on extreme weather, biodiversity and food security.
“A 1.5 degree Celsius world is a fundamentally different world with larger extremes and larger climate damages than a 1 degree C world that we’re more or less in right now, which is fundamentally different than the world before this all started,” said Kim Cobb, the lead author of the report's first chapter, in an interview with The Hill.
“We’re already reeling, clearly, from so many of these impacts that the report highlights, especially in the category of extremes that are gripping these headlines and causing so much damage, but of course the 1.5 degree C world is notably and discernibly worse,” Cobb said.
The report also warns that climate change will increasingly be seen in heat waves, more frequent and intense precipitation and droughts.
The report from the IPCC, which was created by the World Meteorological Organization and the United Nations, stated that increases in greenhouse gas concentrations in the atmosphere since about 1750 were “unequivocally caused by human activities.”
"The fact that the IPCC has agreed — with the agreement of all member countries, 195 member countries — that it is unequivocal that human activity is causing climate change, is the strongest statement the IPCC has ever made," Ko Barrett, IPCC vice chair, told reporters on Sunday.
It said that it’s likely that humans had already caused about 1.07 degrees Celsius of extra warming compared to pre-industrial temperatures between 1850 and 1900.
In addition to the 1.5 degrees of warming, the new report also found that without serious greenhouse gas emissions reductions, global temperatures will rise by a full 2 degrees Celsius compared to preindustrial levels.
It said that if greenhouse gas emissions remain around their current levels in the middle of the century, it’s extremely likely that the planet would exceed 2 degrees Celsius of warming by 2100, but this level of warming is unlikely to be exceeded if the world reaches net-zero emissions around or after 2050 and has net-negative emissions thereafter.
To reach net-negative emissions, the world would need to be absorbing or removing more greenhouse gases from the air than it's emitting into the air.
The report said that while 1.5 degrees Celsius was more likely than not to be reached, even in a low-emissions scenario, surface temperatures may decline back to below this level by the end of the century if net-zero is reached and is followed by net-negative emissions.
In a scenario where emissions continue at the same level they’re at until the middle of the century, the planet is expected to reach by about 1.5 degrees of warming in the near-term, 2 degrees in the mid-term and 2.7 degrees by the end of the century.
“This report is a reality check,” IPCC Working Group 1 Co-Chair Valérie Masson-Delmotte said in a statement.
“We now have a much clearer picture of the past, present and future climate, which is essential for understanding where we are headed, what can be done, and how we can prepare,” Masson-Delmotte added.
It predicts that by the end of the century, temperatures could range from about 1.4 degrees Celsius above pre-industrial levels in a very low emissions scenario to about 4.4 degrees above the baseline in a very high emissions scenario.
"What the report is very clear about is that these choices over the next couple decades are really going to begin to lock in pathways that will have increasingly steep cost functions in terms of climate damages for the rest of this century and beyond," Cobb told The Hill.
The report also warns of serious climate change impacts, saying that for each additional one-half degree Celsius of global warming, there will be “clearly discernible” increases in intensity and frequency of hot extremes like heat waves, heavy precipitation and agricultural and ecological droughts.
It said the extremely hot weather resulting from climate change was very likely, and that droughts and fluctuations in precipitation could be projected with high confidence.
It said that worldwide, daily precipitation events would intensify by about 7 percent for each degree Celsius of warming. It also said the share of hurricanes that are in the most intense categories — categories 4 and 5 — are expected to increase with global warming, as are peak wind speeds.
Increased warming is also expected to worsen permafrost thawing and lack of sea ice. The report predicted that at least one September before 2050 will see the Arctic with practically no sea ice and that this is expected to happen more frequently at higher warming levels.
The report also projected the average sea level around the world would rise during the 21st century.
By 2100, levels could rise between .28 and .62 meters under net-zero scenarios, between 0.44 and 0.76 meters if emissions stay where they are until mid-century and rising between 0.63 and 1.01 meters in a “very high” emissions scenario.
“Climate change is already affecting every region on Earth, in multiple ways. The changes we experience will increase with additional warming,” said IPCC Working Group 1 Co-Chair Panmao Zhai in a statement.
Updated at 10:33 a.m.