For Kids

Younger Kids

Living on Earth is really cool, but sadly humans are making it hotter. It’s a bit like living in a giant greenhouse but with the windows closed. If we were a planet and we went to hospital, the doctors would look at our heartbeat, our temperature, and measure our vital signs. For Earth Scientists are our doctors. Scientists look for evidence of the Earth feeling poorly, and needing to go to hospital. A hotter Earth can lead to lots of people losing their homes from floods, high winds, and fires. This means that lots of people have to go to hospital to get better, or they might no longer have a home to live in, or any food to eat which must be really scary. The scientists can make people and the Earth better again, but they need all of our help to do this.

Older Kids

In the United States of America the space explorers at NASA have written a very good guide for children on climate change. It has lots of moving pictures and videos and looks really cool. Here is a summary taken from the NASA Climate Kids website.

Scientists attribute the global warming trend observed since the mid-20th century to the human expansion of the "greenhouse effect" warming that results when the atmosphere traps heat radiating from Earth toward space.

Certain gases in the atmosphere block heat from escaping. Long-lived gases that remain semi-permanently in the atmosphere and do not respond physically or chemically to changes in temperature are described as "forcing" climate change. Gases, such as water vapor, which respond physically or chemically to changes in temperature are seen as "feedbacks."

Gases that contribute to the greenhouse effect include water vapor, nitrous oxide, carbon dioxide and methane.

On Earth, human activities are changing the natural greenhouse. Over the last century the burning of fossil fuels like coal and oil has increased the concentration of atmospheric carbon dioxide (CO2). This happens because the coal or oil burning process combines carbon with oxygen in the air to make CO2. To a lesser extent, the clearing of land for agriculture, industry, and other human activities has increased concentrations of greenhouse gases.

The consequences of changing the natural atmospheric greenhouse are difficult to predict, but certain effects seem likely:

• On average, Earth will become warmer. Some regions may welcome warmer temperatures, but others may not.

• Warmer conditions will probably lead to more evaporation and precipitation overall, but individual regions will vary, some becoming wetter and others dryer.

• A stronger greenhouse effect will warm the oceans and partially melt glaciers and other ice, increasing sea level. Ocean water also will expand if it warms, contributing further to sea level rise.

• Meanwhile, some crops and other plants may respond favourably to increased atmospheric CO2, growing more vigorously and using water more efficiently. At the same time, higher temperatures and shifting climate patterns may change the areas where crops grow best and affect the makeup of natural plant communities.

The Role of Human Activity

In its Fifth Assessment Report, the Intergovernmental Panel on Climate Change, a group of 1,300 independent scientific experts from countries all over the world under the auspices of the United Nations, concluded there's a more than 95 percent probability that human activities over the past 50 years have warmed our planet.

The industrial activities that our modern civilization depends upon have raised atmospheric carbon dioxide levels from 280 parts per million to 400 parts per million in the last 150 years. The panel also concluded there's a better than 95 percent probability that human-produced greenhouse gases such as carbon dioxide, methane and nitrous oxide have caused much of the observed increase in Earth's temperatures over the past 50 years.

For Grown Ups

In the United Kingdom the government website has a really well written explanation of climate change. For the full details please see the link below. The text below is taken from this website.

https://www.gov.uk/guidance/climate-change-explained

There is clear evidence to show that human activity is significantly augmenting climate change. Measurements show that the average temperature at the Earth’s surface has risen by about 1°C since the pre-industrial period. Some 17 of the 18 warmest years on record have occurred in the 21st century and each of the last 3 decades have been hotter than the previous one. This change in temperature hasn’t been the same everywhere; the increase has been greater over land than over the oceans and has been particularly fast in the Arctic.

The UK is already affected by rising temperatures. The most recent decade (2008-2017) has been on average 0.8 °C warmer than the 1961-1990 average. All ten of the warmest years in the UK have occurred since 1990 with the nine warmest occurring since 2002.

Although it is clear that the climate is warming in the long-term, note that temperatures aren’t expected to rise every single year. Natural fluctuations will still cause unusually cold years and seasons but these events will become less likely.

Along with warming at the Earth’s surface, many other changes in the climate are occurring:

• warming oceans which can be measured as far as 2km down

• melting polar ice and glaciers including sea ice and ice sheets

• rising sea levels which is dependent on greenhouse gas emissions

• more extreme weather events including more intense rainfall

Causes of climate change

Rising levels of carbon dioxide and other greenhouse gases, such as methane, in the atmosphere create a ‘greenhouse effect’, trapping the Sun’s energy and causing the Earth, and in particular the oceans, to warm. Heating of the oceans accounts for over nine-tenths of the trapped energy. Scientists have known about this greenhouse effect since the 19th Century.

The higher the amounts of greenhouse gases in the atmosphere, the warmer the Earth becomes. Recent climate change is happening largely as a result of this warming, with smaller contributions from natural influences like variations in the Sun’s output.

Carbon dioxide levels have increased by about 45% since before the industrial revolution. Other greenhouse gases have increased by similarly large amounts. All the evidence shows that this increase in greenhouse gases is almost entirely due to human activity. The increase is mainly caused by:

• burning of fossil fuels for energy

• agriculture and deforestation

• the manufacture of cement, chemicals and metals

About 43% of the carbon dioxide produced goes into the atmosphere, and the rest is absorbed by plants and the oceans. Deforestation reduces the number of trees absorbing carbon dioxide and releases the carbon contained in those trees back into the atmosphere.

Evidence from past climate change

Ancient ice from the polar ice sheets reveals natural temperature changes over tens to hundreds of thousands of years. Air bubbles trapped in the ice show that levels of greenhouse gases in the atmosphere are closely linked to global temperatures. Rises in temperature match closely with an increase in the amount of greenhouse gases.

These ice cores also show that, over the last 350 years, greenhouse gases have rapidly increased, and are now at levels not seen for at least 800,000 years and very probably longer. Modern humans, who evolved about 200,000 years ago, have never previously experienced such high levels of greenhouse gases.

Natural fluctuations in climate

Over the last million years or so the Earth’s climate has had a natural cycle of cold glacial and warm interglacial periods. This cycle is mainly driven by gradual changes in the Earth’s orbit over many thousands of years but is amplified by changes in greenhouse gases and other influences. Climate change is always happening naturally, but greenhouse gases produced by human activity are altering this cycle.

Volcanic eruptions and changes in solar activity also affect our climate, but they alone can’t explain the changes in temperature seen over the last century.

Scientists have used sophisticated computer models to calculate how much human activity – as opposed to natural factors – is responsible for climate change. These models show a clear human ‘fingerprint’ on recent global warming. The latest Assessment Report from the IPCC said it was extremely likely that most of the observed increase in global temperature since the 1950s is due to human activity.

Climate models and future global warming

We can understand a lot about the possible future effects of a warming climate by looking at changes that have already happened on Earth. But we can get much more insight by using mathematical models of the climate.

Climate models can range from a very simple set of mathematical equations (which could be solved using pen and paper) to the very complex, sophisticated models run on supercomputers (such as those at the Met Office).

While these models cannot provide very specific forecasts of what the weather will be like on a Tuesday in 100 years’ time, they can forecast the big changes in global climate which we could expect to see in the future.

All these climate models tell us that under a scenario of ever-increasing greenhouse gas emissions the world could become up to 4.8°C warmer than the pre-industrial period by the end of this century. Note these are global averages and that temperatures in certain regions, such as the Arctic, would be even higher than this.

At the Paris climate conference (COP21) in December 2015, 195 countries adopted the first-ever universal global climate deal that is due to come into force in 2020. The Paris agreement sets out a global action plan to put the world on track to avoid dangerous climate change by limiting global warming to well below 2°C above pre-industrial levels and pursue efforts towards limiting to 1.5°C. The country commitments we have seen so far represent a dramatic improvement on ‘business as usual’ emissions projections. But these commitments are predicted to give rise to global temperature increases of around 3°C. Further urgent action is needed therefore to put us on track to well below 2°C.

Further Information

NASA has an amazing website here on climate change, showing how the world has changed in photos, with latest scientific evidence and global indicators like carbon dioxide levels and so much more.