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Climate Science Basics
Climate change is one of the most discussed scientific topics of our time. Understanding the basic science helps you make sense of the news, evaluate claims and take part in discussions about solutions. In this lesson you will learn how the greenhouse effect works, what the evidence shows and what the impacts and responses are.
Weather versus climate
- Weather is the condition of the atmosphere at a particular time and place: today’s temperature, rain or wind.
- Climate is the average pattern of weather in a region over a long period, usually 30 years or more.
A single cold day or snowy winter does not disprove climate change, just as one hot day does not prove it. Climate scientists look at long-term trends across the whole planet.
The greenhouse effect
The greenhouse effect is a natural process that keeps Earth warm enough for life.
- Sunlight passes through the atmosphere and warms Earth’s surface.
- The warm surface gives off energy as infrared radiation (heat).
- Greenhouse gases, such as carbon dioxide (CO2), methane (CH4), nitrous oxide and water vapour, absorb some of this heat and send part of it back toward the surface.
Without any greenhouse effect, Earth’s average surface temperature would be well below freezing. The problem is not the greenhouse effect itself, but the enhanced greenhouse effect: adding more greenhouse gases traps more heat and warms the planet further.
Main sources of human greenhouse gas emissions
| Gas | Major human sources |
|---|---|
| Carbon dioxide | burning coal, oil and gas; deforestation; cement production |
| Methane | livestock, rice paddies, landfills, leaks from oil and gas systems |
| Nitrous oxide | fertilisers and some industrial processes |
Methane traps much more heat per molecule than CO2, but it stays in the atmosphere for a shorter time, about a decade on average. CO2 can affect the climate for centuries.
The evidence
Multiple independent lines of evidence point to a warming climate:
- Temperature records: global average surface temperature has risen by more than 1°C since the late 1800s, and recent years have been the warmest in the instrumental record.
- Ice: mountain glaciers are shrinking worldwide, and Arctic sea ice has declined significantly since satellite records began in the late 1970s.
- Sea level: global sea level is rising as ocean water expands when it warms and as land ice melts.
- Ocean heat: the oceans have absorbed most of the extra heat.
- Nature: many species are shifting their ranges toward the poles or to higher elevations, and spring events like flowering are happening earlier in many places.
The scientific consensus
The Intergovernmental Panel on Climate Change (IPCC), which assesses research from thousands of scientists worldwide, concluded in its 2021 report that it is unequivocal that human influence has warmed the atmosphere, oceans and land. Major scientific organisations around the world agree.
Impacts of climate change
- more frequent and intense heatwaves
- changes in rainfall, with heavier downpours in some regions and worse droughts in others
- sea-level rise, threatening coastal communities and ecosystems
- stress on ecosystems, such as coral bleaching caused by marine heatwaves
- effects on food, water and health
Impacts are not evenly shared. Communities with fewer resources, and those in low-lying or drought-prone regions, often face greater risks despite contributing least to emissions.
Responses: mitigation and adaptation
| Strategy | Meaning | Examples |
|---|---|---|
| Mitigation | reducing the causes of climate change | renewable energy, energy efficiency, protecting forests |
| Adaptation | adjusting to current and expected changes | flood defences, heat-resistant crops, early warning systems |
In the Paris Agreement of 2015, nearly every country agreed to aim to limit global warming to well below 2°C above pre-industrial levels, and to pursue efforts to limit it to 1.5°C. Each country sets its own plans to cut emissions.
Example
A coastal city faces rising seas and stronger storms. For mitigation, it installs solar panels on public buildings and improves bus services. For adaptation, it restores mangrove forests and salt marshes, which absorb wave energy and reduce flooding, while also storing carbon and providing habitat.
Discussing climate respectfully
People agree on much of the science but may disagree about which policies are best, because policies involve trade-offs between costs, jobs, fairness and speed. Separating scientific questions from policy questions helps make discussions more productive.
Key takeaways
- Weather is short-term; climate is the long-term average.
- The natural greenhouse effect keeps Earth warm; extra greenhouse gases enhance it.
- Multiple lines of evidence show warming, and the IPCC calls human influence unequivocal.
- Responses include mitigation (cutting emissions) and adaptation (preparing for impacts).
Practice
1. Explain the difference between weather and climate. 2. Describe the greenhouse effect in three steps. 3. Give one example of mitigation and one of adaptation.
Answers: 1 weather is short-term atmospheric conditions; climate is the average over decades. 2 sunlight warms the surface; the surface gives off heat; greenhouse gases absorb and send some heat back. 3 mitigation: for example, switching to renewable energy; adaptation: for example, building flood defences.