What is Climate Change?

Climate change refers to changes in the existing climate conditions and includes events, such as increases in surface temperature and changes in precipitation, which are caused by carbon dioxide (CO2) and other GHGs emitted by anthropogenic activities.

The United Nations Framework Convention on Climate Change (UNFCCC) defines climate change as a change in the climate attributed directly or indirectly to human activity that alters the composition of the global atmosphere, and which is observed over comparable periods, in addition to natural climate variability.

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.

Changes in global surface temperature relative to 1850-1900 (IPCC AR6 WGI-Figure SPM.1; IPCC, 2021)

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).

Globally averaged surface atmospheric CO2 concentration. Data from: NOAA-ESRL after 1980;
the Scripps Institution of Oceanography before 1980 (harmonised to recent data by adding 0.542ppm)
Source: NOAA-ESRL; Scripps Institution of Oceanography; Friedlingstein et al 2020; Global Carbon Budget 2020

You can check the satellite-based global observation data from the following website:

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).

Mechanism of the greenhouse effect.

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.

Global surface temperature changes in °C relative to 1850–1900. (IPCC AR6 WGI-Figure SPM.8; IPCC, 2021) These changes were obtained by combining CMIP6 model simulations with observational constraints based on past simulated warming, as well as an updated assessment of equilibrium climate sensitivity. Changes relative to 1850–1900 based on 20-year averaging periods are calculated by adding 0.85°C (the observed global surface temperature increase from 1850–1900 to 1995–2014) to simulated changes relative to 1995–2014. Very likely ranges (shading) are shown for SSP1-2.6 and SSP3-7.0.

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).

Comparison of future temperature change between SSP126 (Low emissions) and SSP370 (High emissions)

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.

The Earth Simulator 3 in Japan Agency for Marine-earth Science and Technology (JAMSTEC)


What is adaptation?

Climate change adaptation is the process of adjusting to the actual or expected climate and its effects. In humans, adaptation is necessary for mitigating climate change effects, preventing climate change implications, or exploiting beneficial opportunities. In some natural systems, human intervention may facilitate adjustments to the expected climate and its effects.

The key difference between adaptation and mitigation is that adaptation seeks to address the impacts of a changing climate, while mitigation seeks to address the causes of climate change by reducing GHG emissions.

Cyclone shelter in Bangladesh (picture by Takahiro Oyama)

Why is adaptation needed?

The impacts of climate change due to GHGs released from anthropogenic activities affect various sectors worldwide.

Global patterns of impacts in recent decades attributed to climate change. Impacts are shown at a range of geographic scales. Symbols indicate categories of attributed impacts, the relative contribution of climate change (major or minor) to the observed impact, and confidence in attribution (IPCC, 2014).

Where is there information on climate change impacts?

AP-PLAT provides information on climate change impacts in “Climate Impact Viewer.”

More tools for acquiring information on climate change impacts can be found in ClimoKit, a database of scientific data and tools.

What are the types of adaptation alternatives?

Over the years, multiple adaptation alternatives have been identified that include a wide range of actions, as summarized in the following table, which are organized into three general categories: structural/physical, social, and institutional.

Categories and examples of adaptation options (IPCC, 2014)

Category Examples
①Structural/physical Engineered and built environment Sea walls and coastal protection structures; flood levees and culverts; water storage and pump storage; sewage works; improved drainage; beach nourishment; flood and cyclone shelters; building codes; storm and waste water management; transport and road infrastructure adaptation; floating houses; adjusting power plants and electricity grids
Technological New crop and animal varieties; genetic techniques; traditional technologies and methods; efficient irrigation; water saving technologies including rainwater harvesting; conservation agriculture; food storage and preservation facilities; hazard mapping and monitoring technology; early warning systems; building insulation; mechanical and passive cooling ; renewable energy technologies; second-generation biofuels
Ecosystem-based Cross Chapter Box CC-EA, Ecological restoration including wetland and floodplain conservation and restoration; increasing biological diversity; afforestation and reforestation; conservation and replanting mangrove forest; bushfire reduction and prescribed fire; green infrastructure (e.g., shade trees, green roofs); controlling overfishing; fisheries co-management; assisted migration or managed translocation; ecological corridors; ex situ conservation and seed banks; community-based natural resource management (CBNRM); adaptive land use management
Services Social safety nets and social protection; food banks and distribution of food surplus; municipal services including water and sanitation; vaccination programs, essential public health services including reproductive health services and enhanced emergency medical services; international trade
②Social Educational Awareness raising and integrating into education; gender equity in education; extension services; sharing local and traditional knowledge including integrating into adaptation planning; participatory action research and social learning ; community surveys; knowledge-sharing and learning platforms; international conferences and research networks; communication through media
Informational Hazard and vulnerability mapping; early warning and response systems including health early warning systems; systematic monitoring and remote sensing ; climate services including improved forecasts; downscaling climate scenarios; longitudinal data sets; integrating indigenous climate observations ; community-based adaptation plans including community-driven slum upgrading and participatory scenario development
Behavioral Accommodation; household preparation and evacuation planning; retreat and migration, which has its own implications for human health and human security; soil and water conservation; livelihood diversification; changing livestock and aquaculture practices; crop-switching; changing cropping practices, patterns, and planting dates; silvicultural options; reliance on social networks
③Institutional Economic Financial incentives including taxes and subsidies; insurance including index-based weather insurance schemes; catastrophe bonds; revolving funds; payments for ecosystem services; water tariffs; savings groups; microfinance; disaster contingency funds; cash transfers
Laws and regulations Land zoning laws; building standards; easements; water regulations and agreements; laws to support disaster risk reduction; laws to encourage insurance purchasing; defining property rights and land tenure security; protected areas; marine protected areas; fishing quotas; patent pools and technology transfer
Government policies and programs National and regional adaptation plans including mainstreaming climate change; sub-national and local adaptation plans; urban upgrading programs; municipal water management programs; disaster planning and preparedness; city-level plans, district-level plans, sector plans, which may include integrated water resource management, landscape and watershed management, integrated coastal zone management, adaptive management, ecosystem-based management, sustainable forest management, fisheries management, and community-based adaptation

What are the steps for implementing adaptation?

There are three iterative steps for implementing adaptation as given below:
① Scoping: Identify risks, vulnerabilities, and objectives; and establish decision-making criteria.
② Analysis: Identify alternatives, assess risks, and evaluate tradeoffs.
③ Implementation: Implement decisions, monitor, review, and learn.

Climate-change adaptation as an iterative risk management process with multiple feedbacks (IPCC, 2014).