How is the climate changing?
Climate change is more than just what’s happening at the Earth’s surface. Rising greenhouse gases and the excess heat trapped in Earth’s atmosphere are already causing the oceans to rise as well as becoming warmer and more acidic, the world’s ice cover to melt, our weather to become more extreme and the loss or relocation of many plants and animals.
Scientists project all of these impacts will worsen if emissions keep rising but that the worst effects of climate change could be avoided by limiting global temperature rise to 1.5°C.
How does extra heat change our world?
Since the dawn of the industrial revolution, the influence of human activities - primarily burning coal, oil and gas - have caused greenhouse gases to accumulate in the atmosphere, amplifying the natural ‘greenhouse effect’ and warming up the planet.
An estimated 93% of the excess heat trapped by greenhouse gases accumulates in the world’s oceans. Most of the rest goes into melting ice in the Arctic and elsewhere (3%) and heating the land (3%). Only about 1% is stored in the atmosphere.
The additional stored energy causes a huge variety of changes across the Earth, some of which scientists have predicted for decades. The most obvious is that the average temperature at the Earth’s surface has risen by about 1.0ºC since humans started industrialising. Water in the ocean and in lakes is also warming. Ice on land and sea is melting. Sea level is rising due to the expansion of sea water as it warms and extra water entering the oceans from melting ice sheets and glaciers.
There is growing evidence that weather patterns are changing across the world, with most land regions now seeing more frequent heatwaves. While climate change is causing heavier rainfall in many regions, the Mediterranean is experiencing increased drought. Warmer oceans have made hurricanes stronger though the overall number has stayed about the same. Higher seas mean that storm surges are reaching further in land than a few decades ago, causing more damage to highly populated coastal areas, small island states and low-lying communities.
Plants and wildlife are also changing. Species are being forced to adapt or migrate towards the poles and/or to higher altitudes in order to remain within the climatic conditions to which they are best suited. Studies have shown how climate change has already led to local extinctions of some species. The oceans are becoming more acidic and losing oxygen, with consequences all the way up the marine food chain.
Climate changes are happening unevenly across the world. For example, the Arctic region is warming more than twice as fast as the global average. In some parts of the world, such as the Eastern US and Gulf of Mexico, sea level is rising faster than the global average.
As well as affecting natural ecosystems, climate change is already having consequences for humans, livelihoods and wellbeing. Of the global population, 58% live with water scarcity (compared to 14% in the 1900s) due to rising demand from a growing population and climate change. More people and property are being exposed to flooding, which is increasing damages and economic losses. Declining fish stocks, shifts in fisheries and coral reef ‘bleaching’ are leading to lost income and livelihoods for the communities that depend on them.
Future climate change
We’re already seeing the impacts of the 1°C warming we’ve experienced so far as a result of human activity. As long as greenhouse gases keep rising, these impacts will continue to worsen.
The precise impacts that the world sees will depend on how far global temperature rises, and how quickly. What different regions experience will depend on other factors too, such as population growth, infrastructure, economic development and other societal factors.
As a general rule, the higher the temperature, the greater the risk. Or conversely, the lower global temperature rise stays, the more we are likely to avoid the worst impacts of climate change. There is also lower risk of abrupt and irreversible changes, known as ‘tipping points’, such as disintegration of the Greenland and Antarctic ice sheets.
Projections of future climate are made using computer models. These use complex sets of equations to represent processes within the climate system, such as how seawater responds to warming or how plants respond to increasing levels of carbon dioxide.
Some of these processes are well understood, but others are not. For example, clouds can either warm the Earth by providing an insulating ‘blanket’, or cool it by reflecting solar energy back into space. So if a warming climate produces more clouds, that could either amplify the amount of warming or moderate it, depending on where in the atmosphere they form.
Much of the carbon dioxide emitted from fossil fuel burning, the main cause of man-made climate change, endures in the atmosphere for hundreds of years. So a certain amount of further warming is inevitable because of CO2 already emitted into the atmosphere. Even if emissions were stopped overnight, it would take decades for sea level to stop rising because the world’s oceans and ice cover take a long time to react to changes in the atmosphere.
The range of computer models used by the IPCC suggests that strong reductions in carbon dioxide emissions – so that they decline to virtually zero by 2050 - would give a reasonable chance of limiting warming to 1.5°C above preindustrial levels.
However, the world is not on track to meet this goal. Taking into account global climate policy commitments and the current pledges countries have made towards meeting the Paris Agreement, scientists still expect to see around 2.8 C of global warming by 2100.