What causes climate change?
When the average temperature, precipitation, wind, and other weather indicators change significantly over the long term, then climate change is said to have occurred. It can be caused by changes in how much light and heat energy the sun gives out, as well as the amount of volcanic dust present in the atmosphere. These are the natural causes of climate change.
Climate change can also be caused by human, or anthropogenic, activities. For example, humans burn fossil fuels such as coal or oil. This can affect the quality of air by adding to the amount of greenhouses already present in the atmosphere.
Climate change, therefore, has both natural and anthropogenic causes. However, ever since the Industrial Revolution of the late 1800's, anthropogenic factors have exerted an even greater influence on the climate. Humans have been increasingly reliant on industries that give off greenhouse gases, ozone-depleting gases, and air pollutants.
All these affect how much heat energy is trapped in the planet, which, in turn, affects and changes climate systems all over the world.
Is climate change a “new thing”?
No. The historical record shows that there have been remarkable changes in climate in the past. For example, there were times when there was absolutely no ice over the Poles; there were also times when the world's ice sheets extended across what are present day Asia, North America, and Europe. This is a natural process of climate change.
Today's climate change has also been several hundred years in the making. Europe was relatively warm during the 14 century, and then suddenly very cool during the 15th century. The historical record also shows that a Little Ice Age occurred in the 17th-18th centuries, followed by warming, which then accelerated.
The changes that are happening now, however, are more rapid than they were in the past.
Today's CO2 concentrations are higher than they have been in the past few hundred thousand years. This is because human activity depends on the use of fossil fuels. This includes fossil fuel emissions from transportation, agriculture, industry, and power generation. Our increasing use of fossil fuels has therefore increased the amount of carbon dioxide in the atmosphere - which is driving global warming.
Why don't all climate models say the same things about what will happen in the future?
A climate change model makes an educated prediction about future events, while assuming that certain things will happen in the present, and given that some things already occurred in the past.
For instance, a climate change model might focus on the effects of climate change on agriculture, given that we already have had a certain number of intense storms, and assuming that we will have adequate water.
The models that project future climate include assumptions about the decisions that we make on adaptation and mitigation. This is where all models will be uncertain, because there is no way that we can predict what all humans will do, all the time, anywhere in the world.
Because climate change models are predictions made by scientists interpreting the model, and because climate change models have different assumptions that underlie the model, then they will not always be interpreted in the same way. Moreover, all models are estimates.
You can think of the climate system as a dish with many different spices. There are some spices that immediately change the flavor of the dish, say, by altering how other spices contribute to the dish, or by how the dish tastes overall. There are also some spices that contribute only very little to the overall flavor , and no matter how much you add of the spice, you can't completely change the flavor of the dish.
In the same way, we can never paint a completely accurate view of the future because climate is an extremely complex system. There are many different factors in play, and there are so many ways that a climate model can be manipulated in order to explore a thousand possible futures.
What we are sure of, however, is that the more we rely on fossil fuels and non-renewable sources of energy, the more likely it is that we will worsen the effects of climate change in the future.
What do (or don’t) scientists agree on about climate change?
Although scientists do their best to make reliable climate models and conduct experiments carefully, their work is still subject to the scrutiny of their peers. This process of peer review is a way to safeguard scientific work so that scientists can learn from each other and improve their methods.
The process of peer review has been going on for hundreds of years, and it is a healthy way to keep scientists on their toes, so that they don't work on their experiments carelessly, or, worse, fake their findings.
Peer review is also not about 100% agreement. It is normal for scientists to disagree on certain aspects of their science. Scientists are still human, and science is a human activity, so no scientist or scientific work will ever be perfect. When scientists correct each other, it's a good sign that they are thinking critically, and working the way that science was designed.
However, there are a few things that scientists definitely agree on when it comes to climate change. They acknowledge that greenhouse gases, such as carbon dioxide, trap heat. They also agree that people have added much carbon dioxide to the atmosphere ever since the Industrial Revolution. They also agree that the planet is warming, and this phenomenon has negatively affected all living organisms, including humans. Finally, scientists also agree that global warming is happening, and it is primarily due to human activities.