Climate change today is caused mainly by human activities that release greenhouse gases, above all burning coal, oil and gas, along with deforestation and agriculture. These gases trap heat in the atmosphere and warm the planet. Natural factors such as the sun and volcanoes also affect climate, but they cannot explain the warming of the past century. This guide explains what causes climate change, how the greenhouse effect works, how climate change affects people, whether it has any benefits, and what the carbon dioxide record shows.
The Greenhouse Effect, Simply Explained
Sunlight passes through the atmosphere and warms the Earth’s surface. The warm surface gives off heat as infrared radiation. Some gases in the atmosphere, called greenhouse gases, absorb that infrared energy and send part of it back toward the surface, keeping the planet warmer than it would otherwise be.
The natural greenhouse effect is essential: without it, Earth would be frozen. The problem is the enhanced greenhouse effect. By adding more greenhouse gases, people have thickened this heat trapping layer, so more heat stays in the climate system.
The Main Causes of Climate Change
1. Burning fossil fuels
Coal, oil and natural gas are the remains of ancient plants and plankton, carbon stored underground for millions of years. Burning them for electricity, heat, transport and industry releases that carbon as carbon dioxide (CO2), the largest single driver of current warming.
2. Deforestation and land use change
Forests store huge amounts of carbon in trees and soils. Clearing them for farming, ranching or timber releases that carbon and removes a sink that would otherwise absorb CO2 every year.
3. Agriculture
Cattle and other ruminants produce methane during digestion, flooded rice fields release methane, and nitrogen fertilizers release nitrous oxide. Both gases trap far more heat per molecule than CO2, though they are present in smaller amounts.
4. Industry and waste
Cement production releases CO2 chemically, not just from fuel. Landfills produce methane as waste rots, oil and gas operations leak methane, and some industrial gases used in refrigeration are extremely powerful greenhouse gases.
5. Natural factors
Changes in the sun’s output, large volcanic eruptions (which briefly cool the planet), natural ocean cycles such as El Niño, and slow changes in Earth’s orbit have all shaped past climates. But solar output has not risen over recent decades while temperatures have, and volcanic effects last only a few years. The Intergovernmental Panel on Climate Change (IPCC) concluded in its 2021 assessment that it is unequivocal that human influence has warmed the atmosphere, ocean and land, and that global surface temperature in 2011 to 2020 was about 1.1 °C higher than in 1850 to 1900.
Case Study: The Carbon Dioxide Record
The longest direct record of atmospheric CO2 comes from the Mauna Loa Observatory in Hawaii, started by Charles David Keeling in 1958 and now run by NOAA. I charted the annual mean values from NOAA’s Global Monitoring Laboratory and calculated how fast they are rising.
- CO2 rose from 315.98 ppm in 1959 to 421.08 ppm in 2023.
- The rise is speeding up. In the 1960s, CO2 rose by about 0.9 ppm a year (1960 to 1970). In the 2010s it rose by about 2.4 ppm a year (2010 to 2020), nearly three times faster.
- Today’s level is about 50% above the preindustrial level of roughly 280 ppm, my calculation from the 2023 value. Ice cores show levels this high have not occurred for at least 800,000 years.
My take as a biologist: the saw tooth pattern inside each year, which you can see in the monthly data, is the planet breathing: CO2 drops every northern summer as forests grow and rises every winter as leaves decay. That biological signal is tiny next to the long term climb, which tracks fossil fuel use almost exactly. The record also shows why a single good year does not matter much: even when emissions dipped during the 2020 pandemic, the curve kept rising, because CO2 accumulates for centuries.
How Climate Change Affects People
- Heat: more frequent and intense heat waves raise the risk of illness and death, especially for older people, outdoor workers and people without cooling.
- Water: droughts in some regions and heavier floods in others; shrinking glaciers threaten the water supply of mountain regions.
- Food: heat and drought reduce crop yields in many warm regions, and fisheries shift as fish move.
- Coasts: rising seas and storm surges threaten coastal cities, farmland and drinking water.
- Health: the range of some disease carrying insects, such as mosquitoes, is expanding.
The effects on animals and ecosystems are covered in detail in our guide to how climate change affects wildlife.
Does Climate Change Have Any Benefits?
A few, locally and in the short term: longer growing seasons in some cold regions, fewer cold related deaths in some places, newly ice free shipping routes in the Arctic, and higher CO2 can boost the growth of some plants. But these gains are small and uneven compared with the damage from heat, drought, floods, sea level rise and ecosystem loss, and many of them fade as warming continues. The IPCC’s assessments conclude that the overall impacts are negative and grow with every increment of warming.
Air pollution and climate change share many of the same sources, as explained in our guide to the types of pollution.
Frequently Asked Questions
What is the main cause of climate change?
Burning fossil fuels, which releases carbon dioxide. Deforestation and agriculture are the next largest contributors.
Is climate change natural or caused by humans?
The climate has always changed naturally, but the current warming is caused by human activity. Natural factors such as the sun cannot explain the rise since the mid 20th century.
What is the difference between global warming and climate change?
Global warming is the rise in average global temperature. Climate change is broader and includes changes in rainfall, extreme weather, sea level, ice and ecosystems that come with that warming.
Which greenhouse gas contributes most to climate change?
Carbon dioxide, because of the huge amounts released and its long life in the atmosphere. Methane is more powerful per molecule but shorter lived.
How much has the Earth warmed?
About 1.1 °C in 2011 to 2020 compared with 1850 to 1900, according to the IPCC.
Sources
- IPCC (2021), Climate Change 2021: The Physical Science Basis, Summary for Policymakers.
- NOAA Global Monitoring Laboratory, Trends in Atmospheric Carbon Dioxide.
Erzsebet (Eli) Frey is a biologist with a BSc in Biology and an MSc in Ecology from the University of Belgrade. She has field and lab experience across Asia, the Middle East, Europe and South America and uses Python and machine learning on biological data. Based in Serbia, she writes BATAECO and also runs Simply Ecologist and Eco&Stylish.