President Trump appeared to be unaware this week of the existence of a long-standing group of the world's top climate scientists when he asked who "drew" a report predicting a catastrophic scenario for climate change.

The report was written by 91 authors from 40 countries, members of the Intergovernmental Panel on Climate Change (IPCC).  It had 6,000 scientific references and tens of thousands of expert reviewers, including governments, worldwide.

Reporters asked the president on the White House lawn about the document released Monday, which laid out a grim future under almost irreversible climate change. The report found that the world is already seeing consequences from a single degree Celsius (1.8 degrees Fahrenheit) of global warming, with more weather extremes, rising sea levels, and melting Arctic sea ice. The document looked at what would happen at 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial levels.

The goal of the 2015 Paris Agreement was to cap temperature rise at 2 degrees Celsius (3.6 degrees Fahrenheit). The scientists projected that 1.5 degrees would be bad enough, but that a 2-degree rise would be catastrophic. The report's conclusion is that the world is rapidly running out of time to reduce greenhouse-gas emissions.

On Tuesday, Trump said of the report, "It was given to me. And I want to look at who drew it. You know, which group drew it. I can give you reports that are fabulous, and I can give you reports that aren't so good. But I will be looking at it, absolutely."

What is the IPCC?

The Intergovernmental Panel on Climate Change was founded in 1988 by the United Nations Environment Program (UNEP) and the World Meteorological Organization (WMO) to assess what was then an emerging worry about global warming caused by the burning of fossil fuels.

The IPCC does not conduct research. Rather, it reviews what it considers the top scientific information it can find. Its reports are reviewed by scientists, to ensure objectivity. Currently, the IPCC counts 195 countries among its members, including the United States.

It has a regular cycle of reports, and issues special reports when requested. The current special report was requested in 2015 by the U.N. Framework Convention on Climate Change in Paris to look at what would happen under a 1.5-degree rise.  So Monday's report was the culmination of several years of work.

For the new report, the IPCC brought in thousands of scientists from around the world to coordinate the most recent findings on climate science.

Who are the authors of the report?

Of the report's 91 authors, eight are from the U.S. One of them is Haroon Kheshgi, a scientist with ExxonMobil, who helped write a chapter on mitigation.

Robert Kopp, director of Rutgers University's Institute of Earth, Ocean, and Atmospheric Sciences, said that the IPCC is reflective of current thinking, and that scientists volunteer their time to write the reports. Kopp is working as an author on an IPCC report, due in 2021, on sea-level change. If anything, he said, IPCC reports tend to be conservative because there is so much input from varying countries.

"The reports really do represent a collective voice of the climate-science community," Kopp said. "They are are written by consensus. Because it is consensus-driven, the sharp edges tend to get filed down."

What does the report say?

The report says the impacts of climate change are already being felt through weather extremes.

Scientists are concerned that catastrophic events such as Hurricane Michael, now bearing down on Florida; Hurricane Florence last month in the Carolinas; and Hurricanes Harvey, Irma and Maria in 2017 — the costliest tropical cyclone season on record in the U.S. — will become more common as the climate continues to change.

But there is good news, according to the report: Actions are already being taken to limit global warming to 1.5 degrees.

To keep that momentum, however, would require "rapid and far-reaching" transitions in how energy is used in industry, transportation, cities and farms. Global net human-caused emissions of carbon dioxide, the chief greenhouse gas, would need to fall by about 45 percent from their 2010 levels by 2030 to reach "net zero" by 2050. Anything beyond a 1.5-degree rise would require devising ways to remove carbon dioxide from the air. There is no proven way to do that.