The science and impacts of climate change

Why do we hear so much about 1.5°C and 2°C of warming?

These thresholds come from the Paris Agreement, a United Nations treaty signed in 2015 by 196 countries committing them to limit global warming to “well below” 2°C and preferably to within 1.5°C above pre-Industrial levels (meaning levels from around 1850, before mass industrialisation).

2°C used to be the level at which “dangerous” climate change was thought to occur, but we now know that there is no “safe” level and risks increase rapidly with warming. The target of 1.5°C was proposed by a group of small island countries that have the most to lose from rising sea levels under higher levels of warming.

After the Paris Agreement, climate experts at the IPCC produced a Special Report on Global Warming of 1.5°C which concluded that the impacts of climate change get worse with every fraction of a degree of warming. Therefore, we must do everything we can to limit warming to as low a level as possible to avoid the worst impacts.

Read more about where the 1.5°C target came from, and why we’re losing sight of its importance, in this article in The Conversation by Professor Piers Forster.

How long is the planet going to last? I heard that it was 12 years

The “12 years to save the Earth” message came from media headlines about the IPCC Special Report on Global Warming of 1.5°C, which said that CO2 emissions need to fall by 45% by 2030 (12 years from when the report was released in 2018), to stay within 1.5°C of warming above pre-Industrial levels. More recently, climate experts from the IPCC said that global greenhouse gas emissions must peak before 2025 to stay within 1.5°C and that immediate action is needed.

Planet Earth will last a long time and has seen environments much warmer than today in its 4.5 billion-year history. However, anthropogenic (human-caused) climate change will have devastating impacts on biodiversity and human society, and this is partly because the rate at which climate change is occurring is far faster than human society and ecosystems would be able to adapt to naturally. For example, at 2°C warming virtually all corals will die and almost a third of the world’s population will be exposed to extreme heat waves at least once every 20 years (see this explainer from WWF and this interactive chart by Carbon Brief showing and comparing climate impacts at 1.5°C, 2°C and 3°C+).

Is it too late?

The impacts of climate change are already being felt but will get worse the longer we continue to emit greenhouse gases. It is not too late to prevent some of the very worst impacts of climate change: the IPCC and the International Energy Agency have shown that we can limit warming to 1.5°C above pre-Industrial levels if we take immediate and rapid action. At higher levels of warming, the risks of serious illness or death from climate-related extremes (such as heatwaves) increase, but these impacts are not distributed equally and are much more likely to affect people in the Global South who have contributed less to climate change. Even in wealthy countries, many people around the world will experience a lower quality of life, in addition to widespread loss of biodiversity and the destruction of the living world.

When is it too late?

Though it is “virtually certain” that we have already caused irreversible change to some elements of the climate system, we can still limit warming and the impacts of climate change. This is why every fraction of a degree (and every action) matters – we can always do more to prevent the worst impacts of climate change. It is also important to remember that a warming of 1.5°C for a single year does not mean we have failed to meet the 1.5°C target of the Paris Agreement.

Scientists have also identified possible “tipping points” where beyond certain limits ice sheets may melt away, leading to centuries of sea-level rise or species becoming extinct either directly through climate change or indirectly, such as through the loss of habitat and drought. Professor Johan Rockström from the University of Potsdam, Sweden, is a pioneer in understanding these tipping points – you can learn more through his TED Talk and interview and documentary on Netflix called ‘Breaking Boundaries: The Science of Our Planet’. The exact thresholds at which these tipping points are found are uncertain, which is why we need to do everything we can to avoid every fraction of a degree of temperature rise possible.

When are we all going to die?

Human extinction is not expected, but we have to learn to cope in a warmer world, which means cooperating and providing support and resources to the vulnerable and most impacted. Climate change is already contributing to the sixth mass extinction: a report by WWF found populations of wildlife have reduced 60% between 1970 and 2014, and although not all of these losses are driven by climate change, climate change likely played a role.

What are the main sources of greenhouse gases?

Our use of fossil fuels (such as coal, gas and oil) is the main source of greenhouse gas emissions. Climate experts from the IPCC tell us that the three largest sources are fossil fuels used in energy supply, industry and farming. Other large sources come from deforestation, transport, and the construction of our buildings.

We hear a lot about carbon dioxide (CO2), but other greenhouse gases include methane (CH4) and nitrous oxide (N2O) which are the main emissions from agriculture. Different sectors contribute different amounts of these greenhouse gases and it is important to understand the sources and impacts of each.

When and how will we feel the impacts of climate change?

We are already detecting the impacts of climate change here in the UK, like the increasing frequency and magnitude of extreme weather events (heatwaves and flooding), as well as food shortages and effects on food production. Because we import food and other goods, climate change in other parts of the world will also affect the availability and prices of these items in the UK.

Increasing temperatures, frequency of extreme weather and damaging impacts on food and water supplies will make some parts of the world very hard to live in. This will lead to climate refugees having to find somewhere else to live.

Carbon Brief has developed a visualiser to understand the impacts of climate change at different levels of warming and a group of climate scientists have created a tool allowing you to see how you will experience climate change, based on the year you were born and where you are from.