Global Warming Facts, Causes, and Effects

Here's What Happens for Each Degree of Global Warming

Man pushing another man in a wheelchair through the floodwaters of Hurricane Harvey
People make their way out of a flooded neighborhood after it was inundated with rain water, remnants of Hurricane Harvey, on August 28, 2017 in Houston, Texas. Photo:

 Photo by Scott Olson/Getty Images

Global warming is the increase in the average temperature of the world's atmosphere and oceans since the preindustrial age. Since 1880, the earth’s average temperature has risen about 1 degree Celsius or 2 degrees Fahrenheit.


Scientists have three ways to measure global warming. Since 1960, they’ve used satellites. For data since 1880, they also have reliable weather monitoring stations.

For data going back a million years, they drill ice cores from glaciers. These cores reveal the amount of oxygen and hydrogen isotopes for each age. Scientists can calculate the average temperatures from those samples.

Paleontologists can also roughly measure the earth’s temperature from fossil records. The closest comparison is the Paleocene Eocene Thermal Maximum. It was the era between the end of dinosaurs and the rise of mammals. Over 5,000 years, between 4 trillion and 7 trillion tons of carbon were released. The difference is that humans have released the same levels of carbon over hundreds, not thousands, of years.

The temperature rose between 5 C and 8 C, but it took place over thousands of years. At current rates, it will rise by 5 C in just a few hundred years.

As the planet warmed, it triggered a chain reaction. It released reservoirs of solid methane buried in seafloor sediments. Wildfires released more carbon dioxide. It increased global temperatures by at least 41 F. Large animals went extinct and smaller ones thrived. For example, the horse survived because it evolved into a smaller version of itself. It went from the size of a large dog to a small house cat. It took more than 150,000 years for the carbon dioxide levels to recede to more normal levels.

The asteroid that killed the dinosaurs also triggered global warming. Its impact vaporized limestone and incinerated forests. So much carbon dioxide was released that it took 100,000 years for the Earth's climate to return to normal.


All these measurements tell the same story – the temperature is rising faster than at any other time in the Earth's history.

Not only is the temperature rising quickly, but it’s accelerating. Two-thirds of the increase happened after 1975. From 1880 to 2020, the 10 warmest years occurred after 2000, with the last six years being the warmest.

The colder zones are warming even faster than temperate or equatorial zones. In the past 60 years, Alaska has warmed by about 3 degrees Fahrenheit. That's twice as fast as the rest of the United States. 

Global warming causes climate change. That's created more extreme weather, health risks, a rise in the sea level, and higher food costs. If global warming exceeds 2 C, it will create climate destabilization. Melting ice caps and thawing tundra will create a feedback loop that leads to a permanent hothouse Earth.


Global warming is caused by the greenhouse effect. Carbon dioxide and other greenhouse gases trap the Sun's heat radiation and reflect it back to earth. In February 2021, the C02 level was 416 parts per million.

In 1850, the CO2 level was 280 parts per million. Since then, humans have burned colossal amounts of plant-based fuels such as gasoline, oil, and coal. That releases the C02 the plants had absorbed during their lifetimes.


The amount of greenhouse gases already in the atmosphere means that temperatures will keep rising even if we stop emitting today.

The last time CO2 levels were this high was in the Pliocene era. Sea levels were 23.5 meters (about 77 feet) higher, there were trees growing at the South Pole, and the temperature was between 3 C and 4 C higher than today.  It takes time for temperatures to rise in response to greenhouse gases. It's like turning on the burner to heat the coffee. Until greenhouse gases are reduced, the temperature will continue to climb until it’s 4 C higher.

Despite what some say, sunspots do not cause global warming. Neither does El Nino, which is instead worsening because of global warming. In past millennia, warming was caused by shifts in the earth's orbit. That hasn’t happened this time.

Effects of Current 1 C Warming

The last time the planet was approached temperatures this warm was 116,000 to 127,000 years ago, during the Eemian Age. Global average annual surface temperatures were 1 to 2 degrees warmer than pre-industrial levels. The Greenland and Antarctic ice sheets were much smaller, sending the sea level around 6 to 9 meters, or 20 to 29 feet, higher. That's enough to put New Orleans, Miami, and Amsterdam underwater.

Why isn't the sea level that high now? Warming has happened so fast that the ice hasn't had time to fully melt. It's like putting an ice cube in hot coffee, it doesn't melt instantly. Over thousands of years, ice will continue to melt unless the temperature is reduced.

Global warming is already having major effects in four main areas: extreme weather, health risks, sea-level rise, and food inflation. Between 2007 and 2017, it’s cost the U.S. government $350 billion.

Extreme Weather

In July 2018, heatwaves set new temperature records all over the world. Climate scientists were shocked by their severity.

Droughts in North Africa and South America are killing crops and drying up water sources. This is creating a global security threat, as people migrate to survive. Disengaged youth are particularly vulnerable to radicalization. The California drought raised nut and fruit prices. Midwest drought killed off corn crops, raising the price of beef Pests have weakened forests, allowing more destructive wildfires.

From 1980 to 2020, U.S. hurricane damage has exceeded $997.3 billion.

Ironically, rapid Arctic warming increases blizzard frequency in North America. It splits the polar vortex, a zone of cold air that circles the Arctic. That sends cold Arctic air upon New England and Europe. Warmer ocean temperatures add moisture, creating bomb cyclones.

Health Risks

Global warming contributes to 150,000 deaths each year. By 2030, that number will reach 250,000. It climbs to 12.6 million deaths if you add the impact of pollution and extreme weather.

One in every nine people faces hunger caused by crop failure. Heat-related deaths alone kill 650 Americans each year.

Health care costs are higher for 50 million asthma and allergy sufferers. Plants now produce more pollen, including larger and more allergenic "super pollen.” Between 1995 and 2015, the pollen season has increased by 25 days in some areas of North America. By 2040, pollen counts will double by 2040. Stanford University professor Mark Jacobson estimated that 20,000 people die from air pollution for every 1 C rise in global temperatures. 

Disease-carrying pests are spreading, carrying West Nile virus, malaria, and even bubonic plague. From 2004 to 2013, mosquito, flea, and tick-borne illnesses have tripled to 640,000. Lyme disease is now in all 50 states with a 20-fold increase in Maine.

Flooded sewage systems have caused higher rates of hepatitis C, SARS, and hantavirus. Research in Siberia discovered that some of the permafrost doesn't refreeze in the winter. It could be a source of diseases that have been frozen for millennia.

Sea Level Rise

In 2020, Arctic sea ice reached the second-lowest level on record. That has led to rising sea levels and flooding of coastal cities.

In February 2018, North Pole temperatures rose 45 F above normal. The Bering Strait was ice-free. The absence of sea ice contributes to "Arctic Amplification." The dark water absorbs the sun's radiation and further heats the ocean.

In Antarctica, glaciers have been losing their mass at an "unusually rapid" rate. The Pine Island Glacier is thinning by more than one meter per year. In 2015, the continent lost 183 gigatons of ice. That's 36 gigatons more than it lost in 2008.

Food Inflation

North American and European wheat, corn, and rice crops lose up to 25% for each 1 C increase. Global warming increases damage to crops from insects, drought, and heat.

As the oceans warm, they hold less oxygen. Since the 1950s, these "dead zones" have expanded by 4.5 million square kilometers. As a result, many popular species of fish stay near the oxygen-rich surface or head north. Shellfish and coral reef inhabitants can’t move. Oceans are also absorbing carbon dioxide, making them more acidic. That’s killed off half of the world’s coral reefs in the last 30 years.

Longer growing seasons seem to benefit farmers in Alaska, Scandinavia, Canada, and Russia. But early springs are often accompanied by seasonal frost. In addition, plants don’t benefit from the lower levels of winter sunshine. Some also need a long winter to rest and restore their vitality. As a result, they have lower nutritional value.

It’s also become more expensive to drill for oil in Alaska's North Slope. The equipment, buildings, and pipelines are designed to operate on the frozen ground. When it thaws, this equipment doesn’t work well.

Impact of 2 C Warming

Even if the world stopped emitting gases immediately, the Earth's average temperature increase is projected to surpass 2 C by 2100. There is already enough greenhouse gas in the atmosphere to make that happen.

Temperature increases would not be spread evenly. The Arctic would warm by 6 C. Around 85% of the ground in Alaska is permanently frozen year-round. When it thaws, the waterlogged ground becomes soft and collapses. By some estimates, the Arctic could be ice-free during the summer by 2023. Russia plans to use the faster Arctic route to export liquefied natural gas from northwestern Siberia to China. President Putin forecast that Russia plans to ship 80 million tons along that route by 2025. But he, and others who think they will benefit from climate change, are ignoring all the other perils they will face.

The U.S. Southwest could warm by 5.5 C by 2070, creating near-permanent "superdroughts." Almost 50% of the world’s population would be pummeled by extreme heatwaves. About 340 million people could be flooded from rising sea levels by 2050. This would create 200 million climate refugees.

At that temperature, nearly all of the world's coral reefs would die off. That would cost the global economy $1 trillion each year. The reefs support the livelihoods of 500 million people in 50 nations. It also supports many other marine species. Without coral reefs, most of them would go extinct.

In 1975, Professor William Nordhaus first warned about the economic impact of global warming. He predicted that doubling carbon dioxide, as we have, would increase temperatures by 2 C.

Hothouse Earth

A 2 C increase would risk hitting a tipping point that would trigger "hothouse Earth". A large portion of the polar ice caps would melt, increasing sea levels. Droughts, deforestation, and warming oceans would release massive amounts of natural sources of greenhouse gases. This would create a feedback loop that could raise the temperature by 5 C in the long-term.

The thawing of the Arctic permafrost would accelerate, releasing centuries of frozen greenhouse gases. The chain reaction of increased heating and thawing would be unstoppable. The thawing ground would also release twice as much toxic mercury as the rest of all soils, atmosphere, and ocean combined.

Climate Destabilization

Warmer oceans could shift the North Atlantic current away from Europe. Most of Europe is north of the U.S. state of Maine. Without the warm waters of the current, Europe would become as cold as Newfoundland.

Impact of 2.5 C and 3 C Increase

If the global temperature rises by 2.5%, then the world’s gross domestic product would fall 15% from 2010 levels. If it rises 3 C, global GDP would fall 25%. That’s the same as during the Great Depression, but it would be permanent.

Impact of a 4 C Increase

By 2100, the World Bank said the temperature will rise by 4 C if nothing is done. Global GDP would decline by more than 23%.

The U.S. National Climate Assessment said the coldest and warmest temperature extremes would rise as much as 5.5 C, or 10 F, between 2071 and 2100. The sea level would rise one foot per decade, too fast to allow humans to build anew. Once the sea level rises 10 feet, it would flood 12.3 million people.

California and the Great Plains would experience a new, permanent Dust Bowl. Some areas would experience 55 C (131 F) heatwaves.

It will lead to the worst famine since World War II. At least 30 million people are facing famine in 2021, with climate change being a major contributor.

A global investor's group warned it would cost its members $23 trillion in global economic losses. The total damage would exceed $600 trillion, double the total wealth of everyone on the planet. That would shrink the global economy by 23% from what it is today. But GDP would be the least of everyone’s problems.

What You Can Do

Almost three-fourths of Americans believe global warming is real. Almost 65% say it's affecting U.S. weather. Around 45% think it poses a severe threat in their lifetime. More than one in five are very worried about global warming. Another 54% of Americans believe humans cause global warming. Only a third think it's from natural causes. 

In the 2016 Paris Climate Agreement, nations agreed to keep temperatures from reaching an increase of 2 C. They would prefer to keep the increase below 1.5 C. As of March 2021, the Climate Clock shows that, at current rates, we will reach 1.5 C in just over 11 years.

If you want to support efforts to reduce global warming, there are some simple steps you can take today. Cut your heating bill by living in a small house and ensuring it has good insulation. Buy Energy Star home appliances. Eat less meat. Purchase more local products to cut down on emissions from shipping. Turn off lights and unplug appliances when not in use. 

The way you drive and maintain your car can significantly improve mileage. Keep the tires inflated, change the air filter, accelerate slowly after a stop, and drive under 60 miles per hour. That will reduce your emission of greenhouse gases. The April 9, 2007, article in the economist, "Mean Machine," offers more great tips for being an environmentally aware car owner.

You can also become carbon neutral. The United Nations program Climate Neutral Now allows you to offset all the carbon you've emitted by purchasing credits. It helps you calculate your specific carbon footprint. These credits fund green initiatives throughout the world. You can select the specific project that interests you. You can also plant trees. Donations to Eden Reforestation plants trees in Madagascar. That gives the people income, rehabilitates the habitat, and saves lemurs and other species from extinction.

If you want to get more ambitious, you can sue the government. On April 5, 2018, the Colombian Supreme Court ruled that the government must create a plan to combat climate change. The plan must also address deforestation in the Amazon. The Supreme Court referred to the Amazon as an “entity subject of rights.” It gives the river the same rights as a human being. An international human rights organization, Dejusticia, was responsible for the lawsuit creating the ruling.

How Global Warming Helped Trump Win

An article in "Der Spiegel," a German newspaper, predicted how global warming could impact U.S. elections. In 2007, the Nobel Committee awarded Al Gore a Peace Prize to send a signal to U.S. policymakers. It warned the United States to live within its means. 

The article said, "But the Gore factor is having its most powerful effect in a sphere beyond partisan politics, penetrating deep into the insecure American middle class. Its way of life—and this is the real message behind the Nobel Committee's decision—is no longer sustainable."

The newspaper predicted that there would be more green party candidates as a result. At first, the Nobel Committee's message seemed to work. In 2007, the Department of Energy invested $1 billion to spur the biofuels industry to reduce greenhouse gases. Over 100 biofuel factories produced 6.5 billion gallons of ethanol from corn in 2007. Almost 25% of corn production in the U.S. was used for ethanol.

But 10 years later, America's "insecure middle class" rebelled against the "Gore factor," electing Donald Trump to the presidency. One reason many voters chose him was out of a desire for deregulation.

On June 1, 2017, Trump announced that the United States would withdraw from the Paris Climate Accord. His 2018 budget slashed funding for climate change research. It cut the Environmental Protection Agency's budget by 31%. He ordered the EPA administrator to reverse standards on tailpipe emissions. Similar regulatory rollbacks occurred throughout his administration.

Trump and some other Republicans believe sustainable practices will hinder economic growth. But even conservative Newt Gingrich disagreed in his book "A Contract with the Earth." He argued that environmental sustainability and economic prosperity are far from mutually exclusive. He said, "if environmental quality declines enough, the economy won’t be able to function at all.” We are dangerously close to finding out how that happens.

Since taking office, President Biden has begun working to reverse Trump's rollbacks on environmental controls. He has put addressing climate change as one of the central issues of his administration.

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