How can half a degree of warming matter so much?

Ilissa Ocko

This post was co-authored by Monika Barcikowska, a member of EDF's Climate Science team.


  • Half a degree Celsius is just an average: Some regions of the world will experience a lot more.
  • We already see what 1°C warming can do. More warming will exacerbate catastrophic weather events like the Atlantic hurricanes in recent years.
  • Impacts will accumulate if we go from 1.5°C to 2°C, with each half degree adding to the overall impact.

Earth has already warmed by 1 degree Celsius, or 1.8 degrees Fahrenheit, above 19th-century global average temperatures, and we're on our way toward 1.5 °C (2.7 °F) by as early as 2030. The Intergovernmental Panel on Climate Change said in its recent report that we'll face significantly less risk if we halt this trajectory and keep temperatures from reaching 2 °C (3.6 °F).

But the global average temperature is just that – an average. There are parts of the world that will warm less, and some that will warm far more.

In a 2 °C world, land can be two to three times warmer than the global average, and the Arctic may be up to four times warmer at 8 °C (14 °F). 

In parts of Southern Africa, for example, temperatures are already reaching the 2 °C mark to double the average global increase so far, research shows. The region is looking at 40-day stretches of extreme hot spells unless the world keeps overall warming below 1.5 °C.

At the same time, the hottest days are getting hotter as overall warming leads to higher extreme temperatures. There were record heat waves on all four continents this summer as temperatures soared far past normal averages in places like Japan and Sweden.

The seemingly modest change of a half degree, in other words, is really not that modest at all.

Already observed changes are a clue

We don't need models to tell us that future warming will have dire consequences – we've already seen what 1° C can do.

In just the past few decades, rising temperatures have worsened extreme weather events, chunks of ice have broken apart, wildfire seasons are months longer, coral reefs are bleached of their colors, islands have been swallowed by sea level rise, and disease-carrying mosquitoes are spreading to new places. Even sports like hockey and skiing have suffered.

Scientists have established how just 1° C of warming so far triggered these changes. So it's unsurprising that another half a degree, or full degree, will worsen and add to these impacts.

A chain of cause and effect triggers impacts

There are many ways that increased temperatures can affect the world around us – it's a cascading chain of cause and effect that ultimately leads to dramatic impacts.

A warmer world, even at just half a degree Celsius, has more evaporation and thus more water in the atmosphere. Unevenly distributed temperature changes, meanwhile, affect air flow patterns.

Envision a cotton farm in North Carolina that has been around since 1960, with global average temperatures steadily rising by more than half a degree since it grew its first crop. This change has increased evaporation and added moisture to the atmosphere, which for southeastern United States has translated into 30 percent more rain during heavy downpours.

When a hurricane like Florence – already empowered by warmer oceans and higher seas – comes to town and dumps this excess rainfall over the cotton farm, its crops get more flooded and damaged than they did half a century ago. It's how you go from half a degree of warming to economic hardship.

The more extreme weather events we're seeing now – such as higher storm surges from sea level rise and exacerbated drought conditions from dried-out soil – affects society in countless ways.

In fact, an additional half a degree of warming from 1.5° C to 2 °C may cause 10 million more people to be at risk from sea level rise, several hundred million more people to be susceptible to poverty, and a 50-percent increase in the population exposed to water stress. It may double the population exposed to severe heat and cause an additional annual loss of 1.5 million tonnes of global fisheries catch.

However, neither of these warming levels are magic thresholds. Every incremental increase in warming is worse for the planet than the last.

Nor are they inevitable. The IPCC report makes it clear: It's not too late to save the world as long as we act today. With your help we can do this.


For the present administration to know and understand that climate change is an urgent emergency that all countries must fight, but to essentially deny that reality and fail to commit the United States to this immediate goal, is a criminal act and should be punished as a federal criminal offence.

Dennis I Balgemann
October 18, 2018 at 10:37 pm

What about the increasing ice and two years in a row of cooler summers here in the US? Explain that please.

October 19, 2018 at 11:52 am

In reply to by Dennis I Balgemann

This is not true. Just look at California with its forest fires and sub-average snow pack. The Gulf and Atlantic have above-average temperatures that produced above-average hurricane strengths.

David Hurd
October 22, 2018 at 1:20 pm

In reply to by Drinis

It is true summer of 2016 was the hotter than the last two.

evagelos p drinis
October 25, 2018 at 10:12 pm

In reply to by David Hurd

I’ve seen nothing reported about increasing ice levels, or a string of cooler summers. I would be interested in the sources for those observations.

November 28, 2018 at 11:48 am

In reply to by Drinis

Explaining global warming in simple terms is not easy to do. Linking (human-caused) carbon emissions as root cause is not yet possible.

Jim Grillo
October 19, 2018 at 5:38 pm

Hi Jim,

Snow and ice cover has been declining for decades, and United States summers are much hotter than they were 50 years ago. In fact, this past summer (June-September) was our second hottest on record since records began in 1895. And 10 of the 15 hottest U.S. summers on record have occurred in the 21st century. Regardless, climate change is a global, long-term phenomenom. Looking at changes in specific regions over a short period of time does not prove or disprove climate change, as natural cycles can amplify or mask the underlying trend.

Ilissa Ocko
October 25, 2018 at 2:09 pm

In reply to by Jim Grillo

We all are going to hell in a handbasket!

Laura Lea Dodge
October 19, 2018 at 10:50 pm

Climate change is real! Climate change has been, and is bein,g caused by humanity’s use of sequestered carbon fuels! Climate change has been know and understood for over a century! Climate change will be unstoppable in terms of human lifespans if the global community is not 100% carbon free by 2025! The planet will be fine, it’s the people who are screwed!

Thales Nemo
October 23, 2018 at 2:38 pm

The solution is to OUTLAW POLLUTION. The environmental movement needs to unite and organize for THE OFF FOSSIL FUELS ACT (HR 3671). Over 400 groups have endorsed, but how many are WORKING to PASS this bill? 46 Sponsors, led by Rep. Tulsi Gabbard, it mandates 100% renewables by 2035, by requiring Electric Companies to buy only green. Like we "opt-in" to green sources on our electric bill, this makes the whole company do that, nationwide. The question now is HOW FAST the Enviro movement will UNITE to FIGHT. This is no longer a climate science problem, it is a political science issue. Where is the Federal Coalition? State Coalitions? Study Reform Immigration for America, the New York Immigration Coalition. We need CLIMATE infrastructure NOW.

Here's the Bill.
Visit: - to plug in directly, with Food & Water Watch, 350NYC and others.

Todd Fernandez
November 1, 2018 at 11:02 am

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