Comprehension of human-induced climate change has slowly gone from its phase of ridicule and disbelief to awareness and acceptance. Given the deadlines and warnings announced daily by the scientists and the radical plans put forward by policymakers, politicians, and big corporations, it is clear that the effects and the mitigation and adaptation efforts to climate change would most certainly introduce new challenges in our daily life. So, it is essential that we understand some basics of the subject and why it is crucial and morally justified to sacrifice some of our comforts for a better world.

What is climate? How does it change?

　To properly understand climate change, it is essential to know the definition of climate. Climate is the long-term (classically 30 years) average of weather. Thus, daily, monthly, or even yearly weather patterns may not be visible in classical climate statistics. Expanding upon this, we could say that a warm year or a wet month, or a cold week is not climate change. The balance between the input energy from the sun (solar shortwave radiation) reaching the earth's surface and the output energy (longwave radiation) from the planet's surface and atmosphere back to space determines the Earth’s climate. Examples of climate changes induced through former mechanisms are glacial cycles, the little ice age, or the changes induced by volcanic eruptions. Glacial cycles and the little ice age were in response to changes in solar radiation at the top of the earth's atmosphere induced by variation in the earth-sun distance or solar activity. The volcanic eruptions make the atmosphere more reflective, thus changing the net solar radiation at the earth's surface. The best example of climate forcing due to longwave radiation changes is human-induced global warming. Here, increasing concentrations of gases such as carbon dioxide (CO2), methane (CH4), nitrous oxide(N20) changes the composition of the earth’s atmosphere. This change reduces the outward ongwave radiation from the earth and traps more radiation within the atmosphere like the greenhouse in a farm. 

How sure are we about human-induced climate change?

　To prove any scientific hypothesis beyond a reasonable doubt, we need observations supporting our theory and verifiable predictions. In the climate context, that would mean that we need quality-controlled data all over the planet for at least 30 years, which was not always easy. The advent of satellites helped us overcome the issue of data availability and testing predictions to an extent. Furthermore, instead of laboratory experiments in traditional sciences, climate scientists use computer simulations to understand the climate better. In a climate model, we simulate the climate based on observed physical relationships. The increases in computational power availability have enabled us to disentangle the natural variations in climate from anthropogenic climate change. Every five years, the Intergovernmental Panel on Climate Change (IPCC) reviews the latest climate change research and prepares a summary report. The sixth report is being written right now. However, the scientific evidence was already strong enough that the previous report stated, “it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.”

Effects of climate change

　Although it is tempting to attribute all the recent abnormal weather patterns to climate change, confirming that association and understanding the mechanism is not easy, it is relatively easy to understand that a net intake of energy by the earth would increase the lower temperature atmosphere. Nevertheless, this primary change can set off various feedbacks within the climate system that can lead to changes in mean circulation and transport patterns in the ocean and atmosphere. These, in turn, shift the geographical range of plants and animals in both the ocean and land, affecting people making a living by harvesting them. The creeping up of global mean sea level can directly impact the economy and society in most parts of the world. Apart from these mean changes, an increase in the frequency of extreme weather events like heatwaves, floods, droughts, storm surges, and cyclones is also expected due to increased surface temperature.

Further Reading

　The importance of providing coherent and unambiguous scientific inferences led to the creation of The Intergovernmental Panel on Climate Change (IPCC) by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP). Coordinating with scientists all over the world, IPCC publishes comprehensive assessment reports. Reading these reports would strongly recommend, especially the summary for policymakers (SPM), to anyone wishing to learn more about climate change.