Climate Science 101

Climate scientist Dr. Katharine Hayhoe explains the basics of climate change for beginners and those in need of a refresher.

If you’re a journalist new to the climate beat or a reporter wisely looking to bring a climate angle into your stories, this guide is for you. It’s also for anyone else who needs an introduction to climate science without getting too deep into the details. It’s adapted from the work of renowned climate scientist and communicator extraordinaire, Katharine Hayhoe. Be sure to check out Hayhoe’s climate explainer videos, including those from her Global Weirding series as well as her TED and Tedx talks, articles, Q&As, and congressional testimony for more insight.

How is global warming different from climate change?

Global warming refers to the Earth’s most recent period of rising global average temperatures that began in the 1800s following the Industrial Revolution. The term climate change encompasses global warming but also refers to the broader changes that are happening to the planet as a result of global warming, including rising sea levels, melting glaciers, increases in the frequency and/or intensity of extreme weather events like heat waves and heavy precipitation events, and shifts in flower and plant blooming times.

What is the difference between weather and climate?

Weather describes the conditions in a certain place at a certain time, like a sunny day or a week-long cold snap. Climate is the long-term average of weather over decades. Think of it this way: weather is like your mood and climate is like your personality. Of course, even with global warming, cold days still occur. Remember when Senator James Inhofe (R-OK) threw a snowball on the Senate floor in an attempt to reject the reality of climate change? Don’t be fooled by the politician or pundit who rejects global warming when there is snow and ice. A single cold day, month, or even year doesn’t rebut the data that shows the entire planet is warming over climate time scales.

Watch Climate Matters’ Chief Meteorologist Bernadette Woods Placky deliver a climate science 101 rundown in less than 10 minutes.

How do we know the Earth is warming?

Climate scientists track the Earth’s temperature in modern times using thermometers and other scientific instruments at weather stations, ocean buoys, and satellites. There are thousands of thermometers around the world that record temperature each day. Using these, scientists are able to figure out the global average temperature at about two meters above the ground (that’s the height of most thermometers).

Scientists also use “natural thermometers” to see how the Earth’s temperature has changed in the past. Tree rings, ice cores, coral reefs, stalactites, and lakebed sediments: the records preserved in all of these help tell the story of how the Earth’s climate and atmosphere have changed over time.

What this data reveal is dramatic: over the course of modern human civilization, the Earth’s global average temperature has been nearly as stable as that of the human body. It’s gone up and down from year to year, of course; and sometimes there have been longer cool and warm periods over specific regions, such as the Medieval Warm Period and the Little Ice Age over Northern Europe. All of these variations were regional, not global, though, and all of them are minor compared to what we’re seeing now.

Since 1900, the planet has warmed by more than 1 degree Celsius or 1.8 degrees Fahrenheit. Each of the last five decades has been successively warmer than the decade before. The Earth is now warmer than any time in at least 12,000 years. In fact, 19 of the 20 warmest years all have occurred since 2001, with the exception of 1998.

Other evidence of warming includes melting glaciers and land-based ice sheets, shrinking Arctic sea ice, rising global sea level, a longer frost-free season, changes in temperature extremes, increases in atmospheric humidity, and earlier bloom times for many plants and trees.

Wherever we live, we see examples of a warming planet all around us. In western North America, we’re seeing much greater areas being burned by wildfires. In many coastal locations, from the Gulf of Mexico to the South Pacific, we’re seeing stronger hurricanes, typhoons, and cyclones powered by a warming ocean. In many areas of the world, we’re seeing climate change supersize our droughts, making them more frequent and more severe.

While a degree or two does not sound like a lot of global warming, we know that even small changes in the global average temperature can cause major changes. Right now, Earth is running a fever and that fever affects everything we care about — our food, water, health, safety, economy, national security, and even our recreational activities.

Why is the climate changing?

Naturally-occurring carbon dioxide, combined with methane, water vapor and other gases, is what keeps the Earth at the perfect temperature for life. A natural blanket of heat trapping gases surround planet Earth. The sun’s energy shines down and heats the Earth, and the Earth heats up and gives off heat energy. This natural blanket traps a great deal of that heat energy, keeping the Earth almost 60 degrees Fahrenheit or over 30 degrees Celsius warmer than it would be otherwise. Without this natural blanket, we wouldn’t have life on Earth. It would basically be a frozen ball of ice.

So if this blanket is natural, what’s the problem? The problem is that by digging up and burning massive amounts of fossil fuels since the Industrial Revolution, we’re wrapping an extra blanket around the planet that it doesn’t need. This extra blanket traps too much heat that would otherwise escape to space. That’s why the planet is warming.

We know how much extra carbon dioxide humans have produced because we have records of how much coal, oil, and gas we’ve dug up and burned. The carbon in fossil fuels combines with oxygen during the process of combustion, producing carbon dioxide (CO2), a very powerful heat trapping gas. The amount of CO2 in the atmosphere has increased dramatically since the start of the Industrial Revolution.

It’s not the sun, natural cycles, or volcanoes — it’s us

In the past, climate has changed from natural causes: changes in energy from the Sun, massive, sustained volcanic eruptions, and predictable cycles in the Earth’s orbit that drive the ice ages and the warm periods in between have all caused the Earth to be warmer and cooler in the past.

Scientists have examined each of these “natural suspects” to see if they could be the cause of the Earth’s current warming, and the answer is no. According to natural factors, the Earth should be cooling at this time, very gradually. Instead, it’s warming rapidly: and human emissions of heat-trapping gases are entirely to blame.

Burning fossil fuels accounts for about three quarters of heat-trapping gas emissions from human activities. The remaining quarter of emissions come from deforestation, the decay of organic waste, and agriculture. Forests help store carbon, but they release it when they’re destroyed. This is just one of many reasons why the burning of forests is so harmful.

Do scientists agree that climate change is real?

The field of climate science stretches back almost 200 years! For more than 150 years, scientists have known that mining coal and burning fossil fuels produces heat-trapping gases. For more than 120 years, they’ve been able to put numbers on exactly how much the Earth would warm if humans artificially increased carbon dioxide levels in the atmosphere. And it’s been more than 55 years since US scientists first formally warned President Lyndon B. Johnson of the dangers of climate change. Today, the U.S. National Academy of Sciences and most of the leading scientific organizations worldwide have issued official statements acknowledging the reality of and the risks posed by human-caused climate change.

Thousands of scientists around the world are in agreement on the reality of a warming planet. We often hear that 97% of climate scientists agree climate change is real and due to human beings, but in reality that figure is closer to 100%. As the climate scientist Michael Mann recently told “60 Minutes,” “There’s about as much scientific consensus about human-caused climate change as there is about gravity.”

Public confusion over the reality of climate change has largely been manufactured by industry interests and ideologues to sow doubt and prevent climate action. In fact, oil and gas companies such as Exxon have spent decades running costly campaigns to purposely mislead the public about the reality of climate change.

What are the impacts of climate change?

One of the most immediate ways climate change affects people today is through its impacts on weather extremes. As the world warms, climate change is loading the weather dice against us. It’s making many types of events stronger, more frequent, and/or more intense.

Many of the effects scientists long predicted would result from global climate change are happening now, including:

  • More intense, prolonged heatwaves such as the record-breaking ones we’ve seen around the world in recent years, which are becoming stronger and more frequent.
  • Heavier precipitation events, as both rain and snow are increasing. There’s a direct connection to a warming world. Warmer air holds more water vapor, so when a storm rolls in, there’s more water vapor available for that storm to sweep up and dump compared to 50 or 100 years ago.
  • Stronger droughts as warmer temperatures increase evaporation, drying soils and strengthening the high pressure systems associated with drought. High pressure systems direct storms away from the region and suppress the convection that brings rain.
  • Larger wildfires in fire-prone areas such as western Canada and the US, and parts of Australia. Fires are burning greater areas due to the increasing frequency of hot, dry conditions.
  • Stronger hurricanes, tropical cyclones and typhoons that are super-charged by warming oceans, which absorb over 90% of the excess heat produced as climate change warms the Earth. Tropical storms are also intensifying faster and becoming bigger, slower, and with more rainfall in a warmer world.

Through individual weather attribution, scientists can now put a number on the extent to which climate change made a given event more likely or stronger. For example, the 2020 Siberian heatwave that led to a record spike in wildfires across the Siberian Arctic, was made at least 600 times as likely by human-caused climate change, and it’s estimated that nearly 40% of the record-breaking rainfall that fell during Hurricane Harvey in 2017 was the result of human-caused climate change.

Scientists have recently reported on the extent human-induced climate change impacted the 2019-2020 Australian bushfires, the July 2019 heatwave in Western Europe and the large-scale flooding in Southeast Texas from Tropical Storm Imelda.

Why should we care?

Human civilization — our cities, our infrastructure, our agriculture, and how we allocate our water, energy, food, and other resources — developed during a time when climate was relatively stable. The climate changes we are experiencing today are faster and greater than anything humans have ever lived through: and we’re not ready for it.

The climate crisis affects all of us, whether we live in Texas in the US or in Bangladesh. But it does not affect us all in the same way. In the US, as a result of systemic inequities, people of color, Indigenous people, and the poor typically bear the brunt of climate disasters. Globally, poorer countries with very low carbon emissions suffer the most from the carbon emissions from wealthy countries, including the US. According to a recent report by Oxfam America, the richest 10% in the world produce more than half of the world’s carbon emissions, while half of the poorest are responsible for just seven percent of emissions.

Climate change is a threat multiplier, as the US military calls it, that touches everything — from our health to our economy to our infrastructure — and makes our existing problems worse. It increases the risk of crisis and conflict particularly in the poor, unstable, and desperate regions of the world.

The United Nations Intergovernmental Panel on Climate Change (IPCC) warned that one of the main threats to humans as a result of climate change is food insecurity — especially in the Global South, where people rely on small-scale agriculture for food and are more vulnerable to droughts, flooding, and extreme weather. The World Health Organization has estimated that in the 20 years after 2030, climate change will cause “approximately 250,000 additional deaths per year, from malnutrition, malaria, diarrhea, and heat stress.”

The financial burden from a changing climate is also real. In the US, disasters costing more than $100 billion in damages have plagued the country since the 2010s.

Of the four decades since the National Oceanic and Atmospheric Administration began tracking this information, the 2010s accounted for nearly half the total number of disasters and cost, even after adjusting for inflation.

Is it too late to change course?

Yes … and no! First, the bad news: even if there were a magic switch we could flip today to turn off all our coal, oil, and gas immediately, we’d still see some warming from what we’ve already put up in the atmosphere.

But just like when a doctor tells us our arteries aren’t looking great and we need to make some lifestyle changes right away, it’s not too late to change. The quicker we replace our old, dirty ways of getting energy with new, clean sources, like solar and wind, the less temperature change we’ll see, and the lower the risk of serious consequences for all of us.

While it’s not too late to act, the window of opportunity is closing fast. In 2015, world leaders signed the Paris Agreement, which committed them to keep the planet from warming more than 1.5 or 2 degrees Celsius above pre-industrial averages. Even with 1.5 degrees Celsius of warming, we’ll still see significant impacts from climate change, but they will be much less severe than if we continue emitting heat-trapping gases.

So how well are countries doing at keeping their 2015 promises? In 2020, the Climate Action Tracker looked at new climate promises from China and other nations, including carbon plans proposed by US President Joe Biden. If fulfilled, these commitments would mean global temperature rise could be held to 2.1°C by the end of this century. While that’s higher than the Paris Agreement’s target of 1.5° to 2°C, it’s a major improvement from previous estimates that indicated up to 3°C of heating, with disastrous impacts.

What can we do about it?

One of the most important things we as individuals can do is talk about how climate change affects us and what real solutions — positive, beneficial, do-able solutions — look like. According to the Yale Program on Climate Communication, only a third of people in the U.S. hear anyone talk about climate change, even occasionally. And while nearly 80% of people are interested in hearing about climate change in the news, only 25% say that they hear about global warming in the media at least once a week. That’s a more than 50% gap between what people want and what they get!

Here, newsrooms have lots of opportunities. People want to hear the stories of real people who are being affected by climate change and who are making real-life choices today that save money, improve our health, increase our energy independence, create local jobs, and help others. We need to know about choices that together make our lives better than they are today, not worse.

In general, we need climate solutions that will:

  • Generate energy from clean sources that don’t produce carbon dioxide and other heat-trapping gases. Fossil fuels have helped our societies make great progress, but they take us further at our peril. Thankfully we have better, cleaner, and cheaper ways to get the energy we need moving forward, as noted in Rewiring America, a handbook for winning the climate fight.
  • Reduce heat-trapping gas emissions from other important sectors, like agriculture, land use change, industrial processes, transportation, and wastewater treatment.
  • Help us use our resources more efficiently, for example by reducing waste from always-on but inactive devices that are estimated to consume US households $19 billion worth of electricity, equal to the output of 50 large power plants, and cutting food waste (one-third of all the food grown world-wide is wasted). A 2019 study estimated that the US could cut its carbon emissions in half through efficiency alone.
  • Suck some of the carbon dioxide we’ve produced back out of the atmosphere and put it into the soil, where it helps restore the land, or turn it into fuel, or stone, or other useful products.

For a truly inspirational list of viable, practical, and beneficial climate solutions, please see Project Drawdown. Making innovative solutions a reality requires political will, which is why voting is such an important part of the solution. Electing leaders who recognize  the climate crisis and support concrete proposals to limit emissions is key.

As for how to implement these solutions, the answer is simply: at all levels. This includes:

  • National and international solutions such as the recent commitments by big polluting countries and multinational companies to achieve “net zero” emissions by 2050 — meaning greenhouse gas emissions released into the atmosphere are balanced or offset by an equal amount of emissions that are removed. This would bring the goals of the Paris Agreement “within reach” (provided the pledges are fulfilled).
  • Regional solutions implemented across a business, an industry, a city, a state, or a province, meaning everything from retail giant Walmart — which is aiming for 50% clean energy by 2025 and leading an effort to cut a gigaton of carbon from the world’s supply chain — to Houston, Texas, considered the center of the oil and gas industries in the US — which plans to cut their CO2 emissions to meet their Paris Agreement targets. Houston also plans to build 500 miles of new cycle lanes and establish 50 green energy companies by 2025, and plant 4.6m trees in the next 10 years.
  • Simple lifestyle solutions we implement in our own lives, our homes, our schools, our communities, and our organizations, such as churches and congregations that are saving energy and money and taking action through Interfaith Power and Light’s Cool Congregations program.

When it comes to fixing the climate, we need all options on the table and all hands on deck. If you care about yourself, your family, and the future, you already care about climate change. Connecting the dots between what we value and hold dear, and how climate change will impact those things gives us genuine motivation to do our part. This includes holding our elected officials and other leaders responsible to do their part in curbing carbon emissions before it’s too late.

The very best type of solutions are ones that fix other problems at the same time: like increasing clean energy use, which grows the local economy, reduces air pollution, and increases energy security; reducing food waste, which also tackles hunger; and educating women and girls, which reduces infant mortality, increases economic security, and allows them the freedom to choose how many children they have.

The bottom line is, climate change affects us all, no matter how we vote or what we believe. It’s serious and the impacts are here today. The climate crisis requires urgent action now, before it’s too late. But the future is in our hands, and our choices matter.