Still on the fence about how much the planet is warming and how much of it is caused by humans?
Here are the facts to get you up to speed before the CNN Climate Town Hall with 10 of the leading 2020 Democratic presidential candidates on Wednesday.
Carbon dioxide and the greenhouse effect
Carbon dioxide is called a “greenhouse gas” because of its ability to trap solar radiation in the Earth’s atmosphere like a blanket and heat up the planet — acting the same way a greenhouse keeps plants warm and growing.
All of this carbon dioxide is warming the planet.
CO2 naturally occurs in the atmosphere and without it, the planet would be too cold to support life. But human activity, like the burning of fossil fuels for energy, has increased the gas to dangerous levels, increasing the thickness of that blanket to the point that the Earth is heating up.
Before the Industrial Revolution, the levels fluctuated naturally over many thousands of years but had never exceeded 300 parts per million at any point in the last 800,000 years.
In addition to the levels being higher than at any point in human history, the rate at which those levels have increased shows that humans are the cause.
During natural variations in the distant past, carbon dioxide levels took thousands of years to change as much as humans have raised the levels in less than a century.
How much is the planet warming?
The average global temperature is up nearly 2 degrees Fahrenheit.
Scientists have been measuring temperatures around the globe reliably since about 1850 and several independent government and academic institutions — NOAA, NASA,Japan Meteorological Agency, the UK Met Office, among others — track this data to give us global average temperatures.
The agencies use different methods and work separately, but all of these data sets tell us the same thing: Our planet is warming, and nearly every year is warmer than almost all the years before it.
The average global temperature has risen about 2 degrees Fahrenheit, or a little over 1 degree Celsius, since the 1880s. That puts us more than two-thirds of the way to the warming limit of 1.5 degrees Celsius that was set in the Paris climate agreement.
While 2 degrees Fahrenheit might not sound like much, that difference throws a lot of Earth’s processes out of whack. Humans have thrived at a consistent global temperature, and now it’s changing. Think of your body’s temperature: When you have 100-degree fever or higher, it means something isn’t right and it has an effect.
According to NASA, Greenland is losing around 286 billion tons of ice volume per year, while Antarctica shreds about 127 billion tons of ice. Both ice sheets have shown increasing rates of ice loss over the past decade. According to scientists, the summer of 2019 is expected to set the record for the most ice-melt ever recorded over Greenland.
The world’s oceans are warming at an accelerated rate. The ocean is the “memory of climate change” — about 93% of the Earth’s energy imbalance ends up in the ocean.
The oceans have experienced consistent changes since the late 1950s and have gotten a lot warmer since the 1960s, with 2018 being the warmest year on record, followed by 2017, then 2015.
A warmer ocean brings deadly consequences. Warmer waters lead to an increase in rainfall, leading to longer-lasting and more intense storms, stronger hurricanes, dangerous coastal flooding and the loss of sea ice.
If humans don’t do anything to mitigate climate change, warming in the upper part of the ocean will be six times higher by 2081-2100 than total ocean warming in the past 60 years, researchers estimate.