What will the future climate be like?

In the past 100 years, great changes have taken place in the earth's climate, especially recently. Some changes, such as melting glaciers, are visible to the naked eye. Others, such as the change of rain frequency, are not very beautiful. Fortunately, we don't just rely on our eyes to record changes. Scientists have installed instruments all over the world, which can continuously measure the changes of temperature, rain, wind and sunlight. We even installed instruments in space on the satellite, which not only recorded the weather, but also recorded the climate-related properties of the ocean, ice sheet and land, all of which showed the climate of the earth.

In order to better understand the reasons behind the observed climate change, scientists need to do experiments. Suppose a climate scientist is curious about what would happen if the sea salt content in the Pacific Ocean suddenly doubled as it is now. If scientists test this by releasing tons of sea salt into the ocean, the consequences may be disastrous. Instead, scientists have created digital copies of the earth on computers. This copy consists of computer atmosphere, computer ocean and computer land, almost like a video game [1]. This computer copy of the earth is called a climate model.

Climate model is a computer-based model world. Some climate models are more complicated than others.

In the climate model, it is safe to carry out experiments. If scientists want, they can add a pile of sea salt to the ocean or remove all the clouds. Scientists use climate models to carry out realistic and unrealistic experiments to deepen their understanding of the earth's climate.

Before trusting the climate model, scientists want to check whether the model works properly, so they simulate the recent past and compare the model results with the actual observation results. Such an experiment is called historical simulation. This can stop the experiment today by starting the climate model at 1850 and adding pollution (including greenhouse gases and small particles in the atmosphere) every year. Coupled with pollution, it represents human activities, because of the industrial revolution.

This period began in 1850, and the manufacturing process began to release greenhouse gases and small particles into the earth's atmosphere.

, starting from 1850. Using this historical model, we can compare the climate change on the computer version of the earth with that on the real earth, which is measured by our instruments on the earth and in space. If these changes are similar, we know that our climate model is working normally, and we have created a good earth climate model. There are many climate models because there are many ways to describe the complex processes on the earth.

When we look at the results of historical simulation, we usually average the results of many models and present the data as a model. For example, the red line in figure 1 is based on 48 climate models! Figure 1 shows the temperature change data from the industrial revolution to the 20 14 climate model and the actual temperature change measured by the instrument. The data from these models are very consistent with the actual data, and explain what is called global warming.

In the past 150 years, the measured temperature has increased due to the increase of greenhouse gas emissions.

The red line and the black line are very close, so it can be seen that the model shows the evolution of the earth's temperature well. We can also see that the temperature rises with time, first slowly, then faster. This is called global warming.

Accurate climate models can be used not only to estimate the future, but also to guide human actions in the future. Our future climate depends on our future actions. Scientists use climate models to help us prevent dangerous climate change.

Climate change is mainly due to the increase in emissions.

In this case, something is released into the atmosphere.

greenhouse gas

Greenhouse gases are gases that warm the air and cause global warming. The most famous is carbon dioxide.

, especially carbon dioxide (CO2). Climate model is a good tool to evaluate future climate change, because we can use it to test different levels of pollution that may occur in the future. We can't know exactly how much pollution humans will emit in the future, but we can create different stories about what the future may look like. We call these stories scenes.

A potential story about the future. There are many things in our future, depending on the degree of pollution we emit.

One possibility is that the whole world is cooperating to reduce our greenhouse gas emissions and even capture carbon dioxide from the air. This situation is very promising, and we can call it the best situation, or, as many scientists have said, the low emission situation. In the worst case, humans will continue to emit more and more carbon dioxide into the atmosphere in the future, just as we did from 1850 to today.

The experiment using climate model is carried out by changing the amount of pollution in the computer atmosphere every year in the future, either reducing the pollution level to check the best situation or increasing the pollution level to check the worst situation. Climate modeling and historical simulation

A climate model experiment started at 1850 ended today, including pollution emissions. Comparative historical simulation and observation.

As mentioned above, historical simulation starts at 1850 and ends at the present, while future modeling starts at the present and may end at 2 100. Since we don't have any real-world measurements from instruments in the future, it means that when we look forward to the future, we can't compare our model earth with the real earth, which is why only one situation is not enough. We need some climate models, so that we can know the best case, the worst case and the scenarios in between. With this information, we can make the choices that can best shape the future.

Our computer model of the earth tells us that our planet will continue to warm in the coming decades. However, the heat of the earth will directly depend on the lifestyle of all of us, what food we eat, and we will continue to pollute our planet.

One thing all our models tell us is that we need to reduce pollution quickly (Figure 2). If all countries in the world start to reduce carbon dioxide emissions today, the earth will only get warmer 1.8c by the end of this century. In this optimistic situation, we will prevent the sea level from rising too fast, so that our coastal cities will not be submerged. The temperature will not be too hot to grow our food, and we will also limit extreme weather events, such as heat waves and droughts. However, this optimistic best case can only be realized when human beings reduce their emissions to a very low level, ideally zero.

If we continue to pollute for decades before we stop, the earth will surely have a high fever. In these stories of medium and high emissions in our future, the model earth will heat up by 2.7℃ or 3.6℃, just like the human body has a fever. Just a few degrees of warming will make the earth difficult. Glaciers in the mountains and the Arctic will melt completely. Many plants, trees, animals and humans are also difficult to adapt to this hotter world. Of course, we should try to avoid such a story about our future.

In the worst case, not only will we continue to pollute our planet at today's speed, but we will even increase our emissions. In this extreme case, the earth will burn on a large scale and become very hot. Our model earth will heat up by 4.4℃, which will have disastrous consequences for both humans and animals.

The good news is that some countries have started to reduce emissions, so we may not follow this extreme situation. The bad news is that our models and observations tell us that the best-case scenario of low-emission stories is increasingly impossible. Our best estimate at present is that we will move towards a warming of about 3 degrees Celsius in 2 100. Global warming of 3℃ will be higher than the safety threshold of 1.5℃ agreed by politicians all over the world. However, our model also tells us that it is still possible for us to continue to raise the temperature below 1.5℃!

Climate models can be used in experiments that are impossible in real life. These models can be used to estimate the future and the past, but our future story depends on how much pollution humans will emit. The researchers created several scenarios for future emissions. Climate models show that global warming may increase from10 to 4.4°C by 2 100. At present, climate scientists estimate that we will eventually warm the world by about 3 degrees Celsius [2], which will be completely different from today's world. It is important to remember that this estimated warming will not necessarily happen. Even in the low emission scenario of 1.8c, there is still time to make changes to limit climate change. If we work together to reduce greenhouse gas emissions vigorously and quickly, we can keep the earth healthy and livable.