Burley Garcia|Cut emissions quickly to save lives, scientists warn in a new U.N. report

The Burley Garciaplanet is on track for catastrophic warming, but world leaders already have many options to reduce greenhouse gas pollution and protect people, according to a major new climate change report from the United Nations.

The report was drafted by top climate scientists and reviewed by delegates from nearly 200 countries. The authors hope it will provide crucial guidance to politicians around the world ahead of negotiations later this year aimed at reining in climate change.

The planet faces an increasingly dire situation, according to the report. Climate change is already disrupting daily life around the world. Extreme weather, including heat waves, droughts, floods, wildfires and hurricanes, is killing and displacing people worldwide, and causing massive economic damage. And the amount of carbon dioxide accumulating in the atmosphere is still rising.

"Climate change is a threat to human well-being and planetary health," the report states. "There is a rapidly closing window of opportunity to secure a liveable and sustainable future for all."

But there are many choices readily available to policymakers who want to address climate change, the report makes clear.

Those choices include straightforward, immediate solutions such as quickly adopting renewable sources of electricity and clamping down on new oil and gas extraction. They are also more aspirational ones, such as investing in research that could one day allow technology to suck carbon dioxide out of the air.

The authors of the report are not prescriptive. No solution is held up as the "right" one. Instead, scientists warn that there is no time, and no reason, to delay action on climate change. And every potential path forward includes reducing reliance on fossil fuels, the main driver of climate change.

The Earth is really hot and getting hotter

The report lays out sobering facts about the state of the Earth's climate.

The planet is nearly 2 degrees Fahrenheit warmer than it was in the late 1800s, and is on track to exceed 5 degrees Fahrenheit of warming by the end of the century, it warns.

That kind of extreme warming would spell disaster for billions of people, as well as critical ecosystems, and would lead to irreversible sea level rise and mass extinction of plants and animals.

But it is still possible to change course, the report states. If humans can limit warming to no more than 2.7 degrees Fahrenheit (1.5 degrees Celsius), some of the more catastrophic effects of climate change can be avoided. Sea levels would rise a lot less. Heat waves and storms would be less deadly. And many ecosystems on land and in the oceans would be more able to adapt or recover.

To achieve that goal, global emissions would need to be slashed in half by the end of the decade, something the report authors say is still possible if countries around the world quickly pivot away from fossil fuels. Right now, total global emissions are not falling.

A cheat-sheet for world leaders to tackle climate change

Over the last two years, hundreds of scientists working for the U.N.'s Intergovernmental Panel on Climate Change (IPCC) have published three sprawling reports that highlighted the disproportionate effects of climate change on poor people, the need to cut emissions rapidly and the policy options available for doing so. Each of those documents ran hundreds of pages long.

This latest report is the slim summary of all that work: a cheat-sheet for policymakers who face increasing pressure to address global warming.

The timing of its publication coincides with an important deadline under the 2015 Paris Agreement, which aims to keep warming to less than 2 degrees Celsius (3.6 degrees Fahrenheit), and ideally to 1.5 degrees Celsius. The Paris Agreement requires countries to review their progress toward that goal at climate negotiations later this year in the United Arab Emirates.

The hope is that the new report will serve as a shared scientific foundation for those negotiations, as well as a menu of solutions available to world leaders.

"When we talk about climate change it's often really easy to focus on the bad outcomes, the things that are really scary," says Solomon Hsiang, a climate scientist at the University of California, Berkeley who has worked with the IPCC.

He says it's important that policymakers, and the wider public, not lose hope in the face of relentless news about extreme weather and other dangerous effects of global warming. Hsiang's own research has found that millions of lives, and billions of dollars, can be saved by reducing global reliance on fossil fuels, in part because extracting and burning fossil fuels releases enormous amounts of air and water pollution, on top of their damage to the climate.

"Investments in reducing emissions are investments in improving people's health and education and economic opportunities, and protecting the people we care about," he explains.

Poor people are most threatened by climate change

The other big takeaway from the report is that people in developing countries, and poor people around the world, are disproportionately affected by climate change.

"Vulnerable communities who have historically contributed the least to current climate change are disproportionately affected," the report states.

For example, "between 2010 and 2020, human mortality from floods, droughts and storms was 15 times higher in highly vulnerable regions, compared to regions with very low vulnerability," the authors write.

The most vulnerable communities include people who live in low-income countries, low-lying areas and island nations, and Indigenous groups around the world, according to the report.

"We are not all in this together," says Patricia Romero-Lankao, a climate researcher at the National Renewable Energy Laboratory and the University of Chicago who works with the IPCC. "The poorest and most marginalized communities are the most vulnerable, in all cities and in all regions."

Reducing emissions will help protect such communities, now and in the future, says Romero-Lankao.

For example, investing in low-carbon public transit, designing communities to support walking or biking, building homes and other buildings to be resilient and building cleaner power plants can reduce air pollution and save lives in low-lying and low-income neighborhoods that are currently suffering disproportionate damage, the report notes.

One of the biggest topics at international climate negotiations later this year will be how much richer, industrialized countries will pay to help poorer countries transition to clean energy and recover from damage caused by climate change. The industrialized world has historically been the biggest contributor of the pollution now driving climate change.