IPCC Reports are too optimistic

James Hansen is an American climate scientist. Between 1981 and 2013, he worked at NASA Goddard Space Research Institute (GISS), where essential data in terms of climate were produced, and during this time he served as the director of the Climate Research Division of GISS. With his testimony in the US Senate in 1988, he attracted more public attention to the problem of climate change and created scientific awareness. With this and subsequent activism, James Hansen is one of the best-known scientists on climate change. Hansen is an advocate emphasizing the importance of resolute policies and renewable energy sources in tackling climate change.

Despite his retirement from GISS, James Hansen continues his research and effective communication on climate change. In his latest article, Hansen targets the Intergovernmental Panel on Climate Change (IPCC), which is considered an authority in terms of climate science.

The IPCC is often the target of those who do not believe in the climate crisis, particularly fossil fuel companies. The source of this problem is that fossil fuel companies find the IPCC's reports too pessimistic and alarming. The opponents of the climate crisis try to prevent serious measures from being taken by reducing the size of the problem we are facing.

James Hansen, on the other hand, criticizes the IPCC from the opposite angle, for making what is actually happening much more optimistic. Before explaining the criticism, it is helpful to briefly mention the science behind it:

Approximately 342 W/m2 of energy comes from the Sun to the Earth. Some of this energy is reflected back into space, and some is absorbed by the Earth's surface. The absorbed energy heats the Earth's surface, and the Earth radiates this heat back into space. As a result, if the energy coming from the Sun and the energy emitted by the Earth are equal to each other, the surface temperature of the Earth remains constant. This is the basic energy balance of the climate system. Radiative forcing is a measure of the factors that change the energy balance of the climate system and affect the climate, that is, the difference between incoming energy and outgoing energy. If radiative forcing is positive, more energy is trapped in the atmosphere and on the earth, and the climate system gets warmer. In the case of negative radiative forcing, more radiation is reflected and energy is lost, leading to a cooling of the climate system. Natural and man-made processes occurring in the atmosphere and on the earth cause the rays from the Sun to be retained or reflected in the atmosphere. These processes are affected by factors such as greenhouse gases in the atmosphere, aerosols, clouds, and surface properties. 

Radiative forcing is the most important parameter for understanding and modeling climate change in climate science. This forcing factor is taken into account to assess the impacts on climate change and to develop climate models. The numbers 2.6 and 6.0 in different scenarios such as RCP2.6 or RCP6.0, which have been used to model the climate future in recent years, are actually the radiative forcing values that we expect the climate system to have in 2100.

The greenhouse gases we release into the atmosphere cause this radiative forcing value to increase, especially the dust coming out of the chimneys of coal-fired power plants. In recent years, filters installed in chimneys to protect the environment have significantly contributed to environmental health by reducing dust, but the reduction of dust also causes an increase in radiative forcing and global warming. 

Ultimately, what interests us is how the increase in radiative forcing will affect the Earth's average temperature. The approach and general acceptance of the IPCC in this context is that every 4 W/m2 increase in radiative forcing will increase the average temperature of the earth by 3℃. Hansen et al. explain that this value is overly optimistic and that the IPCC uses this value to lead society to optimism about the point of the climate crisis. Considering the radiative forcing caused by greenhouse gases in the atmosphere and the changes in global average temperatures over the last 67 million years, every 5.75 W/m2 increase corresponds to a 7℃ increase in temperature. For this reason, the IPCC's predictions for future temperature rise are considered overly optimistic. Looking at these numbers, it is understood that although the Earth has warmed by 1.2°C on average so far, this warming should actually be 3°C. The reason why the average temperature of the earth has not increased by 3℃ yet is shown by the slower response of the oceans. So, even if we put an end to greenhouse gas emissions now, the Earth's atmosphere will warm by at least 3℃ in the future. For this reason, in addition to putting an end to greenhouse gas emissions, we urgently need to start reducing the amount of greenhouse gases in the atmosphere before the Earth system warms up by responding to the greenhouse gases we have released so far.

Although a little too technical, this article makes it clear that the problems ahead will have far worse consequences than we perceive. Our duty is to listen to what James Hansen and his friends say and act according to the facts, not the most optimistic view; otherwise, the world our children and grandchildren will live in will be much worse than the one before us.