The Intergovernmental Panel on Climate Change (IPCC) does not mince its words when describing the disastrous effect that humans are having on the planet. “It is unequivocal that human influence has warmed the atmosphere, ocean, and land,” reads its latest report.
From heat waves and wildfires to downpours and flooding, 2023 has given us a taste of the impacts we can expect over the coming decades and centuries. In short, it’s not good news. Without very significant reductions in greenhouse gases—beginning immediately—it is very likely that global surface temperatures will exceed the 1.5 degrees Celsius threshold set in the 2015 Paris climate agreement.
Even if we do curtail emissions, sea levels will almost certainly continue to rise throughout this century and may continue to rise for centuries or millennia beyond that. Extreme weather events have become more frequent since 1950 and will become more frequent and more severe as global temperatures increase.
The message could not be clearer: We need to do everything we can to reduce our greenhouse gas emissions right now. Unless we take major action to stop emissions, we’re facing an Earth that is hotter, plagued by more extreme weather, and less hospitable than the already-warmed planet we have today. Here’s everything you need to know about where we are with the climate crisis.
1. There’s more carbon dioxide in our atmosphere than at any time in human history
The Mauna Loa observatory in Hawaii has been tracking Earth’s atmospheric concentration of CO2 since the late 1950s. In 2022, the global average concentration it recorded was 417.06 parts per million (ppm). Preindustrial levels were 278 ppm, which means that humans are halfway to doubling the concentration of CO2 in the atmosphere compared to the period between 1750 and 1800.
CO2 concentrations fluctuate with the seasons, while the speed at which they increase yearly is affected by human behavior. For example, the rising concentration of CO2 in the atmosphere slowed during the early stages of the pandemic when emissions fell, but then rose steeply in 2021 as the world reopened. The annual rise in emissions and atmospheric concentration of CO2 has since slowed down again.The global average CO2 concentration for 2023 is predicted to be 419.2 ppm. The last time Earth’s atmosphere contained this much CO2 was more than 3 million years ago, when sea levels were several meters higher and trees grew at the south pole.
2. We’re accelerating down the path to exceeding 1.5 degrees Celsius of warming
In 2015, the nations behind the Paris Agreement set an ambitious target for keeping global warming below 1.5 degrees Celsius. The latest IPCC report spells out just how difficult it will be for the world to stay under that limit unless we drastically slash emissions now. The report models five different future emission scenarios—from very high emissions to very low emissions—and in each scenario global surfaces are expected to hit at least 1.5 degrees.
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Of the emissions scenarios modeled, only the very low emission scenario estimates that the world would see less than 1.5 degrees of warming by the end of the 21st century. In that scenario, temperatures are likely to overshoot 1.5 degrees of warming between 2041 and 2060 before returning back down to 1.4 degrees of warming by the end of the century. This scenario would require the world to dramatically reduce its emissions with almost immediate effect.
But the point at which the world first steps over the 1.5 degree threshold could be much sooner. According to the World Meteorological Association, there’s a 66 percent chance that the annual average temperature will overshoot 1.5 degrees of warming for at least one year between 2023 and 2027. Indeed, the 1.5 degree limit has already been breached for shorter periods of weeks and months—in 2015, 2016, 2020, and 2023. July 2023 was the hottest month ever recorded, with temperatures breaking records on four consecutive days.
Based on current emissions and policies, the world is likely to experience 2.7 degrees Celsius of warming by 2100.
3. Our remaining carbon budget is tiny
At its core, climate change is really simple to grasp. The more carbon dioxide—and other warming gases—that we put into the atmosphere, the higher global temperatures will rise. Between 1850 and 2021, humans released around 2,500 gigatonnes of CO2 into the atmosphere (1 gigatonne equals 1 billion metric tons). So far, these emissions have led to 1.1 degrees Celsius of warming when compared to preindustrial levels.
To have a 50-50 chance of staying under 1.5 degrees Celsius of warming, we can release only 250 extra gigatonnes of CO2 into the atmosphere—and that includes emissions from the beginning of 2023. To put that in perspective, in 2022 we emitted 36.8 gigatonnes of CO2, and global annual emissions are still yet to peak. In other words, we’ve blown our 1.5 degree budget—it’s just a matter of when, not if, we pass the threshold.
By the same logic, other temperature thresholds have budgets, too. To have a 50-50 chance of keeping temperatures below 2 degrees Celsius of warming, we must emit fewer than 1,350 gigatonnes of CO2 from 2020 onwards. As of mid-2023, roughly only 1,000 gigatonnes of that budget remains.
4. Extreme heat events have become more frequent and severe
You only need to think of recent devastating wildfires in Canada and Hawaii, the scorching temperatures in the southwestern United States, or the evacuation of tourists from Greece to see that climate change is leading to more frequent and more severe hot weather events.
The kind of extreme heat event that had a likelihood of happening once every 10 years between 1850 and 1900 is now likely to occur 2.8 times every 10 years. In a world that hits 1.5 degrees of warming, such events are likely to occur 4.1 times every 10 years. The same is true of once-in-every-50-years events. They’re now likely to occur 4.8 times in 50 years, and in a world that exceeds 1.5 degrees of warming, 8.6 times every 50 years.
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Heavy rain is also more common because of climate change. The kind of heavy one-day rain that 150 years ago would have only happened once every 10 years is now happening 1.3 times every 10 years. In a world warmed by 1.5 degrees Celsius, that will go up to 1.5 times. And as frequency increases, so does severity—we can expect these extreme weather events to be hotter and wetter than those that went before them.
5. Humans have already caused 1.1 degrees Celsius of warming
The latest IPCC report estimates that global surface temperatures are now 1.1 degrees Celsius warmer than they were between 1850 and 1900. Global surface temperatures have risen faster since 1970 than in any 50-year period over the past 2,000 years, and this has been particularly pronounced in recent years.
From 2023 to 2027, the annual average temperature is predicted to range between 1.1 and 1.8 degrees Celsius higher than the 1850–1900 average. There is a 98 percent estimated likelihood that one of the years in this period will surpass 2016 as the hottest year on record.
Global weather systems will be a factor in this. 2023 saw the beginning of an El Niño period, when sea temperatures get warmer in the central and eastern Pacific Ocean with the effect of raising temperatures worldwide and increasing the risk of extreme weather. But just in case there was any doubt, the IPCC’s latest report makes it clear that the principal drivers of rising global temperatures are human-released greenhouse gases.
6. Two-thirds of extreme weather events in the past 20 years were influenced by humans
The number of floods and instances of heavy rain have quadrupled since 1980 and doubled since 2004. Extreme temperatures, droughts, and wildfires have also more than doubled in the past 40 years. While no extreme weather event ever comes down to a single cause, climate scientists are increasingly exploring the human fingerprints on floods, heat waves, droughts, and storms.
Carbon Brief, a UK-based website covering climate science, has gathered data from 400 studies on “extreme event attribution” and has found that 71 percent of all extreme weather events studied in the past 20 years were made more likely or more severe by human-caused climate change—including 93 percent of extreme heat events.
7. Sea levels are rising faster today than ever before
Melting ice sheets and glaciers and warming oceans lead to higher sea levels. Since 1900, sea levels have risen faster than in any preceding century in at least the past 3,000 years, and this is set to continue for a very long time.
The process is also speeding up. Over the past 140 years, sea levels have risen worldwide by 21 to 24 centimeters. But roughly 10 centimeters of that rise has taken place since 1992.
Because oceans take a long time to warm, a lot of sea level rise is already baked in. If warming is limited to 1.5 degrees Celsius, then the global mean sea level will rise between 2 and 3 meters over the next 2,000 years. If warming is limited to 2 degrees Celsius, global mean sea level will rise to between 2 and 6 meters above current levels.
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8. Arctic sea ice is rapidly diminishing
Temperatures in the Arctic are rising faster than almost anywhere else on the planet. Between 2011 and 2020, annual Arctic sea ice reached its lowest level since at least 1850, and late summer Arctic sea ice was smaller than at any time in at least the past 1,000 years. As of 2022, Arctic sea ice cover is decreasing at a rate of 12.6 percent per decade, compared to its average extent during the period from 1981 to 2010.
Under all the future emissions scenarios in the latest IPCC report, the minimum amount of Arctic sea ice will fall below 1 million square kilometers at least once before 2050—making the area practically free of sea ice altogether.
9. The world is getting hungrier and thirstier
For the first time in decades, world hunger is increasing—and climate change is a big driver of this. Extreme weather events from droughts to heat waves affect crop yields and their nutritional value, and some crops will become unviable in certain areas. Under heat stress, animals will become less productive and more liable to pests and disease, which might become more frequent and spread.
Across Africa, where many countries struggle with food insecurity, agricultural productivity has decreased 34 percent because of climate change. By 2050, the risk of hunger and malnutrition could rise by 20 percent worldwide because of the effects of climate change.
Crops, animals, ecosystems, and humans also depend on water—and already the UN estimates that roughly half the world’s population experiences water scarcity for part of the year. Over the past 20 years, climate change has intensified this shortage by lowering the water stored on land.
Water quality is also worsened by climate change, which accelerates urban migration, making water sources more polluted. It also causes flooding, droughts, and higher water temperatures, which can increase the amounts of sediments, pathogens, and pesticides in water.
10. Average wildlife populations have dropped by 60 percent in just over 40 years
The average size of vertebrate populations (mammals, fish, birds, amphibians, and reptiles) declined by 69 percent between 1970 and 2018, according to the biennial Living Planet Report published by the Zoological Society of London and the WWF. That doesn't mean total animal populations have declined by 69 percent, however, as the report compares the relative decline of different animal populations. Imagine a population of 10 rhinos where nine of them died—a 90 percent population drop. Add that to a population of 1,000 sparrows where 100 of them died—a 10 percent decrease. The average population decrease across these two groups would be 50 percent even though the loss of individuals would be just 10.08 percent. And between 1 and 2.5 percent of animal species have already gone extinct.
Whatever way you stack the numbers, climate change is a factor. An international panel of scientists backed by the UN argues that climate change is playing an increasing role in driving species to extinction. It is thought to be the third biggest driver of biodiversity loss after changes in land and sea use and overexploitation of resources. Even under a 2 degrees Celsius warming scenario, 5 percent of animal and plant species will be at risk of extinction. Coral reefs are particularly vulnerable to extreme warming events; their cover could be reduced to just 1 percent of current levels at 2 degrees Celsius of warming.