Global warming is the steady rise in Earth’s average temperature caused mainly by human activities that release greenhouse gases into the atmosphere. Since 1750, industrial activities have increased the concentration of carbon dioxide in the atmosphere by nearly 50%, and in 2024, atmospheric CO2 hit a record 422.5 parts per million. This extra carbon dioxide, along with other gases, traps heat near Earth’s surface like a thick blanket, making the planet warmer than it should naturally be.
How the Greenhouse Effect Works
Earth naturally stays warm enough for life because of something called the greenhouse effect. The sun’s energy reaches our planet as light and heat. Some of that heat bounces back toward space, but certain gases in the atmosphere absorb it and send it back down to the surface. This natural process keeps Earth’s average temperature at about 15°C (59°F), which is comfortable for humans, animals, and plants.
The problem starts when human activities add too much of these heat-trapping gases to the atmosphere. The “blanket” gets thicker, less heat escapes, and temperatures climb. That extra warming is what we call global warming.
The Main Greenhouse Gases
Several gases are responsible for trapping heat, but three matter most when it comes to human-caused warming:
- Carbon dioxide (CO2): Released when we burn coal, oil, and natural gas for electricity, transportation, and industry. It is the single biggest contributor to global warming. In 2022, about 60% of electricity in the United States still came from burning fossil fuels.
- Methane: Comes from livestock digestion and manure, rice farming, landfills, and leaks during oil and gas production. Natural gas itself is 70% to 90% methane, so even small leaks add up quickly.
- Nitrous oxide: Produced mainly by fertilizer use in agriculture and by burning fossil fuels. Its concentration in the atmosphere has risen by 18% in the last 100 years.
Water vapor, ozone, and a group of factory-made chemicals called chlorofluorocarbons also act as greenhouse gases, though their sources and behaviour differ.
What Causes Global Warming
Human activities are responsible for almost all of the increase in greenhouse gases over the last 150 years. The biggest source is burning fossil fuels. Every time a car runs on petrol, a power plant burns coal, or a factory uses natural gas, CO2 is released into the air. Transportation alone is one of the largest sources of direct greenhouse gas emissions, with over 94% of transport fuel coming from petroleum.
Deforestation is the second major cause. Trees naturally absorb CO2 from the atmosphere. When forests are cut down for farming or construction, that stored carbon is released, and fewer trees remain to absorb future emissions. Industrial processes that convert raw materials into products also release greenhouse gases through chemical reactions, not just fuel burning.
The Intergovernmental Panel on Climate Change, a global body of scientific experts, has concluded that it is “unequivocal” that human activities are driving the increase in CO2, methane, and nitrous oxide since the industrial era.
Effects of Global Warming
Rising Sea Levels
Global sea levels have already risen about 21 to 24 centimetres (8 to 9 inches) since 1880. The rate of rise is accelerating: it more than doubled from 1.4 millimetres per year during most of the 20th century to 3.6 millimetres per year between 2006 and 2015. In 2023, the global average sea level set a new record high. Two things drive this rise: glaciers and ice sheets melting and adding water to the ocean, and ocean water expanding as it gets warmer.
Higher seas cause flooding in coastal cities, erode shorelines, and push saltwater into freshwater supplies that communities and farms depend on. High-tide flooding is now 300% to more than 900% more frequent than it was 50 years ago. Even if greenhouse gas emissions are reduced significantly, sea levels are projected to rise at least 30 centimetres (one foot) above 2000 levels by the end of this century.
Melting Glaciers
Glaciers around the world are shrinking. A striking example is the Gangotri glacier in the central Himalayas, one of the largest glaciers in India and the source of the river Ganga. Between 2005 and 2017, Gangotri retreated at an average rate of about 12 metres per year, and its retreat rate nearly doubled from the 2005–2010 period to the 2010–2017 period. Neighbouring glaciers in the same region are also retreating, though at slower rates.
Extreme Weather and Ecosystems
Warmer temperatures fuel stronger storms, longer droughts, and more intense heatwaves. Coastal ecosystems like mangroves and coral reefs face stress from rising water levels. Fish and wildlife habitats shift, affecting both biodiversity and the fisheries that communities rely on for food and income.
Global Warming vs. Climate Change
People often use these two terms as if they mean the same thing, but they are not identical. Global warming specifically refers to the rise in Earth’s average temperature due to increasing greenhouse gases. Climate change is the broader term: it includes global warming plus all the other long-term shifts in precipitation, wind patterns, and seasons that result from a warming planet. In short, global warming is one part of climate change, not the whole picture.
How Global Warming Can Be Reduced
Slowing global warming requires cutting the amount of greenhouse gases we release. The most impactful step is shifting from fossil fuels to renewable energy sources like solar and wind power for electricity and heating. Reducing dependence on petrol and diesel vehicles by using public transport, electric vehicles, or cycling also helps lower emissions.
Planting trees and protecting existing forests is equally important because trees pull CO2 out of the air and store it. Managed forests in the United States, for example, currently absorb enough carbon to offset about 13% of the country’s total greenhouse gas emissions. Carbon capture technologies, which remove CO2 from the atmosphere through engineered systems, are also being developed.
Stabilizing temperatures at current levels would require reaching what scientists call a “carbon-neutral society,” where people remove as much carbon from the atmosphere as they emit. This demands large-scale changes in energy systems and infrastructure, going well beyond individual actions. Governments, industries, and communities all need to work together to make that transition possible.