Is the climate really changing?

Yes, the climate is changing. The global surface temperature was 1.09 °C higher in 2011–2020 than in 1850–1900. Extreme weather events, such as heatwaves, droughts, and floods, are being observed more frequently.

What causes climate change?

Climate change is caused by anthropogenic activities. When the concentration of GHGs, such as carbon dioxide (CO2) released by various anthropogenic activities, increases in the atmosphere, the greenhouse effect increases the surface air temperature and other climate factors, such as precipitation and solar radiation.

GHGs are gaseous components of the atmosphere, caused by both natural and anthropogenic factors. They absorb and emit radiations at specific wavelengths within the spectrum of terrestrial radiation emitted by the Earth's surface, atmosphere, and clouds. This property of absorbing and emitting radiation contributes to the greenhouse effect. Water vapor (H2O), carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), and ozone (O3) are the primary GHGs occurring in the Earth’s atmosphere. Moreover, multiple GHGs, such as halocarbons and other chlorine- and bromine-containing substances, which originate only through anthropogenic sources, are addressed under the Montreal Protocol. In addition to CO2, N2O, and CH4, the Kyoto Protocol addresses the occurrence of sulfur hexafluoride (SF6), hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs).

You can check the satellite-based global observation data from the following website:
https://data2.gosat.nies.go.jp/gallery/L4B/concmov/concmov.html

The solar energy absorbed by the Earth’s surface is emitted as thermal radiation from the land and ocean. Later, most thermal radiation is absorbed by the atmosphere, including clouds, and radiated back to the Earth. This is called the greenhouse effect. Without the natural greenhouse effect, the average temperature at the Earth’s surface would be below the freezing point of water. Thus, this effect facilitates the survival of organisms. However, anthropogenic activities, primarily the burning of fossil fuels and clearing of forests, have considerably intensified the natural greenhouse effect, consequently, causing global warming (IPCC, 2007).

What about the future?

The increase in the global mean surface temperatures for 2081–2100 relative to 1850–1900 is projected to range from 1.0 °C to 5.7 °C.

These ranges are associated with uncertainties of future projections in socio-economic pathways and climate models (see ‘How is future climate projected?’ section). In the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), the scientific community assessed the climate response to five scenarios that include the possible future development of anthropogenic drivers of climate change that have been studied previously. The scenarios include those with high and very high GHG emissions (SSP3–7.0 and SSP5–8.5, respectively) and with CO2 emissions that are approximately twice the current levels by 2100 and 2050, respectively, scenarios with intermediate GHG emissions (SSP2–4.5) and CO2 emissions maintained near current levels until the mid-century, and scenarios with very low and low GHG emissions and CO2 emissions declining to net zero around or after 2050, followed by varying levels of net negative CO2 emissions (SSP1–1.9 and SSP1–2.6, respectively) (IPCC AR6 WGI, 2021).
The Fifth Assessment Report of the IPCC used a set of four scenarios denoted as representative concentration pathways (RCPs). They are identified by their approximate total radiative forcing in the year 2100 relative to 1750: 2.6 W m-2 for RCP2.6, 4.5 W m-2 for RCP4.5, 6.0 W m-2 for RCP6.0, and 8.5 W m-2 for RCP8.5. These four RCPs include one mitigation scenario leading to a low forcing level (RCP2.6), two stabilization scenarios (RCP4.5 and RCP6), and one scenario with very high GHG emissions (RCP8.5).

How to acquire data on future climate projections?

ClimoCast is a tool that allows users to check future regional climate projections and compare major emission scenarios and climate models.

How is future climate projected?

Future climate is projected using “climate models,” which are numerical representations of the climate system based on the physical, chemical, and biological properties of its components, their interactions, and feedback processes, and account for some of its known properties.

More than 100 climate models have been developed in universities and institutes worldwide. The differences among the climate models produce the ranges of future climate projections, even under the same GHG pathway.

High-performance computers, such as super computers, are mostly used for future climate projections because climate models include multiple mathematical equations.