The terms ‘global warming’ and ‘climate change’ are often used interchangeably, but there are important distinctions between the two. As the amount of greenhouse gases in the atmosphere increases, the planet’s temperature rises – as scientists have observed around the world. This is global warming. But the temperature of the atmosphere controls much of the behaviour of the climate. So an increase in global temperature causes other changes, such as rising sea levels, melting ice and shifting rainfall patterns. The term ‘climate change’ describes these knock-on effects resulting from global warming, as well as the warming itself.

As the planet warms, sea level rises. This is caused partly by thermal expansion and partly by melting land-based ice. Mountain glaciers and ice sheets contribute to rising sea level when their meltwater flows into the oceans. Scientists measure sea level using both tide gauges and satellite instruments called altimeters. Altimeters fire radar pulses down to Earth. By recording the time it takes each pulse to bounce off the ocean and return to the satellite, scientists can calculate the water height. Global average sea level rose steadily over the 20th century – at about 2 cm per decade. Recent measurements show the rate has accelerated to 3 cm per decade.

Scientists keep track of glaciers all over the planet, recording their length and the volume of ice they contain using both ground measurements and satellite data. We’d expect glaciers to melt in a warmer world. But a few glaciers aren’t melting, despite rising temperatures. Some glaciers are in areas of extreme cold such as central Antarctica, where even several degrees of warming wouldn’t push local temperatures above freezing. Since a warmer world leads to more precipitation, such glaciers can even increase in size by accumulating more snow. However, measurements show that nine out of ten glaciers worldwide are melting and shrinking.

Both poles have ice caps, but the Arctic and Antarctic are very different. The Arctic is an ocean surrounded by land, while Antarctica is a continent. The Antarctic is isolated from the rest of the world both by the ocean and by a circle of strong winds, which have intensified in recent decades because of the ozone hole. These factors have prevented ice loss in the central Antarctic, although the ice around its edges, especially in the Antarctic Peninsula, has recently shown dramatic changes. In contrast, summer sea ice in the more fragile Arctic has retreated and southern parts of the Greenland ice sheet have begun melting rapidly.

About 20% of land in the northern hemisphere is permanently frozen, mostly far north in Arctic regions. Much of this ‘Arctic tundra’ has been frozen for thousands of years. But now significant areas are thawing. Temperatures are rising faster in the Arctic than in the rest of the world. Warming air warms the ground below. When ground temperature rises above freezing, tundra begins to thaw. Scientists have observed more and more patches of soggy ground appearing in places once permanently frozen solid. As tundra thaws, methane bubbles trapped inside it escape. Scientists have measured significant increases in methane release in the Arctic.

Plants and animals depend on their environment and respond to any changes in their local climate. Recently, in temperate climate zones, animals have been breeding earlier, birds nesting earlier and some farmers have started planting their crops earlier. Some birds that normally migrate to warmer areas for the winter have been staying put, apparently satisfied with local temperatures. Even insects aren’t immune from the effects of climate change. Butterflies and bumblebees, lured out of hibernation by warmer weather, have recently been spotted in the UK as early as December – they usually wouldn’t emerge until January or February. All these changes are consistent with a long-term warming trend.

Debora Iglesias-Rodriguez investigates what effects increasing ocean acidification will have on tiny marine plants – the basis of many ocean ecosystems and fundamental players in the global carbon cycle. ‘My team uses state-of-the-art laboratory techniques to measure changes in proteins, genes and rate of carbon production,’ says Debora. But when not in the lab, Debora regularly conducts research at sea, often in extreme weather conditions in the remote polar regions, which are thought to be particularly susceptible to ocean acidification. ‘When I was at sea in Antarctica a storm held us for hours. We had sheets of ice flying towards us, as we were surrounded by icebergs.’

• NASA: Changes in the Arctic Ice
• Koshland Science Museum
• IPCC FAQ