Covid-19 has shaken much of human society yet threat posed by global warming has not gone away. Human activities have increased carbon dioxide emissions which drive up temperatures. Extreme weather and melting polar ice are among additional possible effects.

The Earth’s average temperature is about 15C , it has been much higher and lower in the past.  There are natural fluctuations in the climate but scientists say temperatures are rising faster now than at many other times.  This is linked to the greenhouse effect which describes how the Earth’s atmosphere traps some of the Sun’s energy.

Solar energy radiating back to space from the Earth’s surface is absorbed by greenhouse gases and re-emitted in all directions.  This heats both the lower atmosphere and the surface of the planet. Without this effect, the Earth would be about 30C colder and hostile to life.

Scientists believe we are adding to the natural greenhouse effect, with gases released from industry and agriculture trapping more energy and increasing the temperature (known as climate change or global warming).

Greenhouse gas with the greatest impact on warming is water vapour, this however, remains in the atmosphere for a few days only.

Carbon dioxide (CO2) persists for much longer. Only so much can be soaked up by natural reservoirs such as the oceans and it would take hundreds of years for it to return to pre-industrial levels.

Most man-made emissions of CO2 come from burning fossil fuels. When carbon-absorbing forests are cut down and left to rot, or burned, that stored carbon is released, contributing to global warming.

Since the Industrial Revolution began in about 1750, CO2 levels have risen more than 30%. The concentration of CO2 in the atmosphere is higher than at any time in at least 800,000 years.

Other greenhouse gases such as methane and nitrous oxide are also released through human activities but they are less abundant than carbon dioxide.

The world is about one degree Celsius warmer than before widespread industrialisation, according to the World Meteorological Organization (WMO).  Apparently the last 5 years have been the warmest on record.

Across the globe, the average sea level increased by 3.6mm per year and most of this change was because water increases in volume as it heats up. Melting ice is now thought to be the main reason for rising sea levels. Most glaciers in temperate regions of the world are retreating and satellite records show a steep decline in Arctic sea-ice since 1979.

The change in the global surface temperature between 1850 and the end of the 21st Century is likely to exceed 1.5C, most simulations suggest.

The WMO says that if the current warming trend continues, temperatures could rise 3-5C by the end of this century.

There is uncertainty and speculation about how great the impact of a changing climate will be.

It could cause fresh water shortages, dramatically alter our ability to produce food, and increase the number of deaths from floods, storms and heatwaves. This is because climate change is expected to increase the frequency of extreme weather events – though linking any single event to global warming is complicated.

Poorer countries, which are least equipped to deal with rapid change, could suffer the most.  Plant and animal extinctions are predicted as habitats change faster than species can adapt. And the World Health Organization (WHO) has warned that the health of millions could be threatened by increases in malaria, water-borne disease and malnutrition.

Global warming will cause further changes that are likely to create further heating. This includes the release of large quantities of methane as permafrost – frozen soil found mainly at high latitudes – melts.

Responding to climate change will be one of the biggest challenges we face this century.