What is Climate Change?

“Climate change is a long-term shift in the "average weather conditions of a region", such as rainfall, temperature, or windiness. Climate change means that the range of conditions expected in many regions will change over the coming decades. This means that there will also be changes in extreme conditions.

The climate varies naturally from year to year and decade to decade. This is caused by natural processes linking the atmosphere, ocean and land, as well as variations in heat output from the sun. In addition to changes in climate that are caused by natural climate variability, climate change can be caused by human activity. The kind of climate change we are experiencing now is being caused primarily by these human factors.” (Environment and Climate Change Canada^[1])

The Earth’s atmosphere contains many different gases, some of which trap heat. These are called greenhouse gases (GHGs), the main ones are carbon dioxide, methane and nitrous oxide. GHGs can come from both natural and artificial sources.  Climate change is caused by an increased concentration of GHGs in the atmosphere. GHGs trap heat on its way to space and act like a greenhouse or a layer of insulation, resulting in the overall warming of the Earth^[2]. This natural process is called the greenhouse effect and has also been compared to a blanket or a jacket trapping heat and warming the Earth.

Since the mid 20^th century, GHG concentrations in the atmosphere have been increasing at an unprecedented rate, causing the blanket of GHGs around the Earth to thicken. Scientists agree this increase in GHGs is due to emissions from human activities such as burning fossil fuels (coal, oil and gas), landfills (methane) and land-use activities like deforestation, the clearing of land for agriculture, industry and other human activities^[3].

“Human activities are estimated to have caused approximately 1.0°C of global warming above pre-industrial levels and are likely to reach 1.5°C between 2030 and 2052 if it continues to increase at the current rate“ (IPCC, 2018^[4]). As a result, the Earth is becoming warmer, and weather patterns, like the amount of rain or snow in a given season or the occurrence and intensity of various weather extremes, are changing.  
 

^[1] Environment and Climate Change Canada, 2020.  Climate Change Concepts.

^[2] Climate Atlas of Canada, 2019.  Greenhouse Gases. Greenhouse Gases | Climate Atlas of Canada

^[3] NASA, 2021.  The Causes of Climate Change. Global Climate Change: Vital Signs of the Planet. Causes | Facts – Climate Change: Vital Signs of the Planet (nasa.gov)

^[4] IPCC, 2018: Summary for Policymakers. In: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)]. World Meteorological Organization, Geneva, Switzerland, 32 pp.