ILULISSAT, GREENLAND - JULY 20:  An iceberg floats through the water on July 20, 2013 in Ilulissat, Greenland. As Greenlanders adapt to the changing climate and go on with their lives, researchers from the National Science Foundation and other organizations are studying the phenomena of the melting glaciers and its long-term ramifications for the rest of the world. In recent years, sea level rise in places such as Miami Beach has led to increased street flooding and prompted leaders such as New York City Mayor Michael Bloomberg to propose a $19.5 billion plan to boost the citys capacity to withstand future extreme weather events by, among other things, devising mechanisms to withstand flooding.  (Photo by Joe Raedle/Getty Images) (Photo by Joe Raedle/Getty Images)
Undeniable climate change facts
02:24 - Source: CNN

Watch CNN’s live town hall on the climate crisis featuring 10 Democratic presidential candidates tonight beginning at 5 p.m. ET.

CNN  — 

Not sure how we found ourselves in this climate crisis?

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.

shishmaref carbon dioxide chart

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 past five years have been the five warmest years since 1850 and 18 of the hottest 19 years have occurred since 2001. The warming trend has rapidly increased since the 1970s.

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.

glaciers melt before your eyes extreme ice survey climate change orig mss_00001518.jpg
See glaciers melt before your eyes
01:24 - Source: CNN

Polar ice is melting

Ice is disappearing from both poles at an increasing rate.

Climate change is occurring the fastest in the Earth’s polar regions, where temperatures are rising more than twice as fast as the planet as a whole.

This is causing major changes is the polar landscape – namely melting ice both in the oceans (sea ice) and the ice sheets in Greenland and Antarctica.

With each decade, there’s about 13% less ice cover. The volume of sea ice is less than half of what it was 20 years ago.

The impact of the lack of ice is showing itself in places such as Alaska, where a lack of ice is leading to fish and animal die-offs and coastal flooding.

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.

Global Warning: Explore Greenland’s ice melt

Sea levels are rising

The most widespread impact from climate change is rising sea levels around the globe.

A combination of melting ice sheets, glaciers and an expansion of the water as it heats up has caused the global average sea level to rise by more than 8 inches since 1900, with almost half of that rise coming in the last 25 years.

Projections show that oceans will rise on average by 1 to 4 feet across the globe by 2100, which would expose 30 to 60 million people worldwide to flooding, assuming we can keep global warming to 1.5 degrees Celsius.

But we do not have to wait until 2100 to see the impacts of sea level rise.

Communities in South Florida are already flooding many times per year during everyday high tides, and they are struggling with the costs to combat the rising tides.

Man tries to avoid ocean water that has spread onto this Miami Beach street during a high tide. The City of Miami Beach is in the middle of a five-year, $400 million storm water pump program and other projects that city officials hope will keep the ocean waters from inundating the city as the oceans rise even more in the future.

Oceans are warming

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.

The climate crisis impacts your health

The climate crisis could “halt and reverse” progress made in human health over the past century, experts say.

Rising global temperatures could lead to many more deaths than the 250,000 a year between 2030 and 2050 the World Health Organization predicted just five years ago.

Higher temperatures bring more bug-borne diseases and cases of malaria, diarrhea, heat stress, heart defects and malnutrition.

Food shortages could become a serious issue.

About 1% of food calories have already been lost from global food production due to rising temperatures. That means a serious loss of food calories for about 50 million people.

The rising CO2 levels have also had a negative impact on the nutritional value of certain crops such as rice, and the climate crisis has reduced crop yield.

It has also negatively impacted floral development, meaning that the pollinators – bees and butterflies – that rely on that pollen are put in jeopardy by the climate crisis.