The world’s climate has been experiencing significant changes during recent decades compared with the more distant past. These recent changes in climate affect the species and geography of our planet in many ways, are already having a significant impact on human life, and are set to become more powerful and frequent as time goes on.
The term climate change refers to changes in the expected patterns of climate behaviour according to records and research. Climate change therefore would include (for example) a series of lower-than-usual temperatures year on year as well as higher than usual temperatures, and would also include phenomena such as less predictable weather and more variation in seasonal norms, and more extreme forms of weather than expected, such as deeper droughts, worse floods, stronger winds, etc.
Scientific observations worldwide about climate change are brought together and assessed by the Intergovernmental Panel on Climate Change (IPCC).
Greenhouse gases (GHGs) are called so because, when the earth’s atmosphere contains a higher concentration of GHGs, the effect is that the atmosphere keeps more of the sun’s heat close to the surface of the earth, like the glass of a greenhouse. But when the earth’s atmosphere contains a lower concentration of GHGs, the surface temperature of the earth drops slightly because less of the sun’s heat is retained. Without some greenhouse effect, the earth would on average be about 33 degrees cooler than it is now (below freezing).
So a certain amount of greenhouse gas in the atmosphere helps keep the Earth’s average temperature above freezing. The major naturally occurring greenhouse gases which do this are water vapour; carbon dioxide (CO2); methane (CH4); and ozone (O3).
Mostly, when we refer to GHGs we mean CO2 and, to a lesser extent, CH4, which is produced in smaller quantities than CO2 but is about twenty-one times more powerful as a greenhouse gas.
Climate Change Mitigation
- Without additional mitigation efforts beyond those in place today, and even with adaptation, warming by the end of the 21st century will lead to high to very high risk of severe, wide-spread and irreversible impacts globally. Mitigation involves some level of co-benefits and of risks due to adverse side effects, but these risks do not involve the same possibility of severe, widespread and irreversible impacts as risks from climate change, increasing the benefits from near-term mitigation efforts.
- There are multiple mitigation pathways that are likely to limit warming to below 2°C relative to pre-industrial levels. These pathways would require substantial emissions reductions over the next few decades and near zero emissions of CO2 and other long-lived greenhouse gases by the end of the century. Implementing such reductions poses substantial technological, economic, social and institutional challenges, which increase with delays in additional mitigation and if key technologies are not available. Limiting warming to lower or higher levels involves similar challenges but on different timescales.
- Mitigation options are available in every major sector. Mitigation can be more cost-effective if using an integrated approach that combines measures to reduce energy use and the green-house gas intensity of end-use sectors, decarbonize energy supply, reduce net emissions and enhance carbon sinks in land-based sectors.
- Effective mitigation responses will depend on policies and measures across multiple scales: international, regional, national and sub-national. Policies across all scales supporting technology development, diffusion and transfer, as well as finance for responses to climate change, can complement and enhance the effectiveness of policies that directly promote adaptation and mitigation.