The Earth’s climate

The climate has a profound influence on all our daily lives and has shaped the history of life on Earth. Climatic conditions are determined by the atmosphere, oceans, land, ice and the life on our planet acting in concert under the power of the Sun.

Earth’s atmosphere forms a layer as thin in relative terms as the skin of an apple. It is mostly made up of nitrogen and oxygen, but also contains smaller amounts of other gases. These include those commonly referred to as greenhouse gases which trap the Sun’s heat and keep the Earth warm enough for life to flourish.

Satellites orbiting the Earth and monitoring stations on the ground show that concentrations of greenhouse gases in the atmosphere are increasing, in particular carbon dioxide. This is leading to rising temperatures and disruption to the climate.

We are already seeing dramatic impacts: altered weather patterns, reduced snow and ice and a rise in sea levels.

These impacts threaten food and water supply, people’s health, security and economic activity, as well as wildlife and the natural world. If we act now to tackle climate change, we will support progress towards a more prosperous, secure and sustainable future. But if we don’t act immediately, this could all be at risk.

A warming world

Records from thousands of weather stations across the world, and ocean data from ships and buoys, show the temperature measured at the Earth’s surface has increased substantially over the past century, and especially over the last fifty years. Certain regions, in particular the Arctic, have seen much more warming than others.

Some years have always been warmer or cooler than others. This is because natural factors can cause year-to-year and decade-to-decade temperature variations. These natural factors include changes to the strength of the Sun, the impact of volcanic eruptions and climate cycles such as the El Niño phenomenon.

Nevertheless, the three decades from 1980 to 2010 all showed record warmth compared with previous decades. Since the turn of the millennium, the world’s temperature has typically been more than 0.75°C warmer than it was 150 years ago in Victorian times and in 2015 it reached 1°C warmer.

Other observations from around the world, including warming of the oceans from the surface to depths and reductions in ice and snow cover, provide further evidence that planetary-scale warming is taking place.

Melting ice and rising sea levels

The warming has dramatically reduced Arctic sea ice. In 2016 and several other recent years, at the end of the summer melt season, the sea ice covered an area less than two-thirds of that at the end of the twentieth century. Just to put that in perspective, that’s a drop equivalent to the area of the United Kingdom, Ireland, France, Spain, Germany and Italy put together. The melting of this floating ice does not raise sea levels, but change on this scale can alter weather across Europe, Asia and North America.

In addition, as the world has warmed, the water in the oceans has expanded, many mountain glaciers have retreated and ice sheets in Greenland and Antarctica have shrunk. These changes have raised sea levels, as long-term measurements of tide gauges and recent satellite data show.

The effects of sea-level rise are felt most acutely when storm surges occur. Worryingly, many of the world’s existing and developing megacities, including Shanghai, Jakarta and Mumbai, are located in vulnerable coastal regions. The flooding which hit New York City in 2012 during Hurricane Sandy showed the damage that storm surges can cause to critical infrastructure.

For now, the Thames Barrier protects London from flooding, but if significant sea-level rise occurs, expensive reinforcement will eventually be required. For many other cities, such defences would be either impossible or simply too costly to build.