As the southeastern United States was hammered by an unexpectedly strong hurricane, the world’s climate experts released a report last week examining what is happening to the planet’s climate as a result of global warming.

Climate changes that are resulting from the burning of oil, coal and gas are measurably harming the planet.  Since the beginning of the Industrial Age the world has heated up by 1.8°F on average compared to preindustrial times.  The effects are already becoming painfully clear: the fastest decline in Arctic sea ice in 1,500 years, more than eight inches of sea level rise since 1880, and more damaging extreme weather due to climate change.

For decades, scientists – including those working for the oil, gas and coal industries – have warned that rising atmospheric concentrations of greenhouse gases from the burning of fossil fuels risk harming the climate, increasing ocean acidity, the frequency of extreme weather events and posed a threat to the health of all species – including humans.  But when the world met in Paris three years ago, it seemed that keeping the temperature within 3.6°F of pre-industrial levels, although seriously damaging, would probably leave Earth a tolerable, habitable place.

The current greenhouse gas emission rate puts the planet on path to reach 5.4°F of warming by the end of the century, even if every country meets its goals under the Paris agreement.  Global greenhouse gas emissions are set to rise this year.  Yet new report, issued by the Intergovernmental Panel on Climate Change a panel that convenes the world’s climate experts, says that the world has a critical 12-year window to make substantial progress in reversing climate change.

The report was depressing.  Unless drastic changes are made in the world’s economy and a resulting radical reduction in the amount of greenhouse gas emissions emitted from human activities, we will see unprecedented devastation.

The new 700-page report, the work of 133 authors, is a comprehensive review of the global evidence that drew on more than 6,000 peer-reviewed research articles.  The overarching conclusion is that temperature rise will exact a huge toll on lives, natural systems, and the economy.  Fighting to keep warming in check — which will include radically and rapidly reducing coal and oil consumption, among other things — will save lives, the food supply, and homes.

The report’s blunt and ominous conclusion:  Unless aggressive actions are taken now, as early as the year 2040, the world will be experiencing worsening food shortages and wildfires and a mass die-off of coral reefs.

To prevent that dangerous level of warming, the report said, greenhouse gas emissions must be reduced by 45 percent from 2010 levels by 2030, and 100 percent by 2050.  The IPCC found that, by 2050, use of coal as an electricity source would have to drop from nearly 40 percent today to between 1 and 7 percent.  Renewable energy such as wind and solar, which make up about 20 percent of the electricity mix today, would have to increase to as much as 67 percent.

Given that the report operates on the consensus of so many scientists, its projections and conclusions are typically conservative.  It is far more likely that the “tipping point” will occur earlier than the year 2040.

Nothing like this has ever happened in recorded history.  Humans are destroying the climate in which they live, at a rate that may devastate humans and other species.  Yet there are no indications that the ideologues and partisans who control the national government are willing to do anything about it, other than advance policies to make the situation even more dire.

There is no easy way out.  We have to stop thinking that technology will save the day without serious trade-offs, that the world will somehow dodge the catastrophic consequences of global warming, that actions won’t come without having to pay for it, either now or in the not-so-distant future.

The world must act, and it must act now.  But collective action on an issue this big requires true leadership by key actors.

Americans must lead the world on this.  Our elected officials – federal, state, and local – must pledge to act, not talk about acting, but act now.