Water supports all life on earth (IPBES, 2019). Every single organism on the planet, every single thing we eat and drink, depends on water to survive. Many complex processes shape our climate, but fundamentally, climate change is a story of water: where it is and where it isn’t, whether or not there is too much or too little, how it functions within the climate system, and how all these factors impact life on the planet. The distribution, movement, amount, and location of water is the primary cycle through which we experience the impacts of climate change and weather (Baede et al., 2001).

The climate system is dynamic and interactive made up of the atmosphere, the ocean and freshwater systems (hydrosphere), ice and snow (cryosphere), soils and land (land surface), and the biosphere (Baede et al., 2001). The water cycle circulates the same amount of water continuously over various timescales (Eagleson, 2000; National Research Council, 2012). While the amount of water in the system doesn’t change, it is always moving and changing states, from vapour to liquid to ice, moving around the atmosphere, evaporating from our oceans and freshwater systems, cycling through the land and biosphere through the trees and soil (Aguado & Burt, 2010; Eagleson, 2000). In some places, it accumulates as snow, freezes, and forms sea ice, glaciers, and ice sheets that reflect radiation from the sun. Ice sheets, glaciers, oceans, and groundwater act as long-term storage systems (Stocker et al., 2013; Aguiado & Burt, 2010). Most water on earth is stored in the oceans, which makes the available freshwater all the more essential to land-based life forms, like humans, that depend on it (USGS, n.d.; IPBES, 2019). 

Feedback Effects

Water vapour is considered the most powerful greenhouse gas because it accounts for a large percentage of warming due to the greenhouse effect (Cook, 2021). Water vapour is an amplifier of warming, but C02 and other greenhouse gases are the drivers. Water vapour concentrations are controlled by temperature, not the other way around. Warm air holds more moisture. A small change in temperature from C02 emissions is amplified by water vapour and enhances the heating effect. The warmer the air, the more evaporation from land and oceans occurs, which puts more water vapour into the atmosphere. This is a positive feedback effect in which water vapour amplifies the warming effect of other GHGs that humans emit (Baede et al., 2001; Cook, 2021; Emmanuel, 2020; Stocker et al., 2013).

The cryosphere, which is made up of sea ice, ice sheets, glaciers, and permafrost, influences the climate is due to its reflectivity, known as its “albedo” (Baede et al., 2001; Emmanuel, 2020). Light coloured surfaces, like bright white snow and ice, reflect more of the sun’s energy, like a mirror (Figure 2). This has a cooling effect on temperatures across the globe when albedo is high. (de Montreuil, Heidenheim, Hunter & Paul, 2021).

Warming from increasing GHGs in the atmosphere causes snow and ice to melt, reducing the amount of energy reflected away from Earth. When snow and ice melt, darker surfaces with lower albedo, like ocean water and land surface, are exposed. Those darker surfaces then absorb more of the sun’s energy, which enhances warming and further melts more snow, ice, and permafrost. This is another positive feedback in the climate system (de Montreuil et al., 2021; Emmanuel, 2020).

Some of the most important feedbacks in the climate system involve water: water vapour amplification, ocean circulation, and ice/snow albedo feedback.

Human influence on the climate through GHG emissions has warmed the earth already, and rapid changes have occurred on a global scale that has affected the atmosphere, hydrosphere, cryosphere, and biosphere  (IPBES, 2019). Impacts on the water cycle are already affecting weather and extreme events globally, including heavy precipitation events, tropical cyclones, and droughts (IPCC, 2021). These changes will impact ecosystems and communities in different ways. With atmospheric temperatures and circulation patterns shifting, climate change will affect where precipitation falls, in what form (e.g. snow or rain, etc.), and how much. It is expected that there will be substantial differences in the patterns of precipitation from region to region (IPCC, 2018). Climate change brings water-related impacts through flooding and drought, from either too much precipitation or not enough at the right place and the right time of year. Coastal communities are at additional risk due to storm surge and sea-level rise.

A warming climate creates all kinds of changes to the climate system and water cycle. Climate change mitigation (reducing our effect on the climate system), while necessary, will not be a sufficient response to the climate problem. We also need to take bold steps toward adapting to the changes we know are coming, by considering things like intense rainfall events, flooding, droughts, sea-level rise, and lack of precipitation when planning communities, infrastructure, buildings, etc.

Understanding how water functions within the climate system and how water and weather are affected by a warming planet due to human activities must also consider issues of equity and justice. Climate change is exacerbating adverse effects on ecosystems, biodiversity, and human well-being across the world, but we are not all impacted equally (Boyd, 2019; IPBES, 2019; IPCC, 2018 [D]). Climate-related impacts disproportionally affect marginalized people that have contributed least to the problem (Boyd, 2019). In populations already affected by things like resource depletion, conflict, and poverty, climate change brings with it additional stressors, threatening food and water supplies due to drought and flood risks (Boyd, 2019). As we take action on climate change it is critical to consider vulnerable populations who are experiencing negative impacts to their human rights, livelihoods, and health to a much greater extent than the people who have contributed most to the problem in the first place.

References

Aguado, E., & Burt, J. (2010). Understanding weather and climate (5th ed.). Pearson Education Inc.

Baede, A., Ahlonsou, E., & Schimel, D. (2001). The Climate System: An overview. In: Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change (p. 881). Cambridge University Press. https://www.ipcc.ch/site/assets/uploads/2018/07/WG1_TAR_FM.pdf

Boyd, D. (2019). Safe Climate: A Report of the Special Rapporteur on Human Rights and the Environment (p. 25). UN Human Rights, Office of the High Commissioner. https://www.ohchr.org/Documents/Issues/Environment/SREnvironment/Report.pdf

Bush, E., & Lemmen, D. (Eds.). (2019). Canada’s changing climate report. Government of Canada. http://publications.gc.ca/collections/collection_2019/eccc/En4-368-2019-eng.pdf

Cook, J. (2021). Explaining how the water vapor greenhouse effect works. Skeptical Science.  https://skepticalscience.com/water-vapor-greenhouse-gas-intermediate.htm    

de Montreuil, L. Heidenheim, L., Hunter, E., Paul, A. (2021). Ice & climate change: understanding Arctic ice-albedo. Royal Roads University. https://docs.google.com/presentation/d/1T3cFPsoxqFj8Jz4kHubPs315EfneMi8HuU6WZQ05hZo/edit#slide=id.ge773f25937_1_22

Eagleson, P. (2000). The Role of Water in Climate. Proceedings of the American Philosophical Society, 144(1), 33-38. Retrieved from http://www.jstor.org/stable/1515603

Emmanuel, K. (2020). Climate science, risk & solutions: Climate knowledge for everyone. Massachusetts Institute of Technology. https://climateprimer.mit.edu/

IPBES. (2019). Summary for policymakers of the global assessment report on biodiversity and ecosystem services of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. S. Díaz, J. Settele, E. S. Brondízio E.S., H. T. Ngo, M. Guèze, J. Agard, A. Arneth, P. Balvanera, K. A. Brauman, S. H. M. Butchart, K. M. A. Chan, L. A. Garibaldi, K. Ichii, J. Liu, S. M. Subramanian, G. F. Midgley, P. Miloslavich, Z. Molnár, D. Obura, A. Pfaff, S. Polasky, A. Purvis, J. Razzaque, B. Reyers, R. Roy Chowdhury, Y. J. Shin, I. J. Visseren-Hamakers, K. J. Willis, and C. N. Zayas (eds.). IPBES secretariat, Bonn, Germany. https://doi.org/10.5281/zenodo.3553579 

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 (pp. 24). Cambridge University Press. https://www.ipcc.ch/sr15/chapter/spm/

IPCC. (2021). Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf

National Research Council. (2012). Challenges and Opportunities in the Hydrologic Sciences. The National Academies Press.

Stocker, T., Qin, G., Plattner, L., Alexander, S., Allen, N., Bindoff, F., Bréon, J., Church, U., Cubasch, S., Emori, P., Forster, P., Friedlingstein, N., Gillett, J., Gregory, D., Hartmann, H., Jansen, B., Kirtman, R., Knutti, K., & Krishna Kumar, P. (2013). Technical Summary. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press.

USGS. (n.d.). Oceans and Seas and the Water Cycle. USGS Water Science School. https://www.usgs.gov/special-topic/water-science-school/science/oceans-and-seas-and-water-cycle?qt-science_center_objects=0#qt-science_center_objects

Wood, R., & Jackson, L. (2020). Could the Atlantic Overturning Circulation ‘shut down’? Carbon Brief.  https://www.carbonbrief.org/guest-post-could-the-atlantic-overturning-circulation-shut-down 

The evidence is unequivocal. We live in a warming world, as evidenced by a steady increase in global average surface temperatures measured over the past 150 or so years (IPCC, 2013). 

Right. But the climate has always changed. What makes this so different?

First, let’s dive into a little history because understanding the past is important for understanding our present as well as our future. 

We have instrumental temperature records from the past 150 years, giving us detailed data on temperatures over that period, particularly since the 1970s (Figure 1) (Emanuel, 2020).

We also have paleoclimate reconstructions of climate that reach back millions of years into earth’s climate history and these show the natural warming and cooling cycles (particularly over the past 800,000 years) that occur due to orbital factors that have allowed the development of ice sheets in the mid to high latitudes based on earth’s distance and orientation with the sun (Figure 2) (Emanuel, 2020, p. 19-20).

These cycles are many thousands of years long and while the initial warming that occurs coming in and out of an ice age initially tends to rise and fall relatively quickly, the rate of warming over the past century is approximately 10x the average rate of warming coming out of an ice age, and that rate is expected to continue increasing over time (NASA, 2010). In fact, according to those natural climate cycles and relative to the past 10,000 years, earth temperatures were quite stable and moving toward a very slow cooling trend in the mid to high latitudes of the Northern Hemisphere for the last five thousand years. Earth’s average surface temperature has risen about 1-degree Celsius since the late 19th century, a change driven largely by increased carbon dioxide emissions into the atmosphere through the burning of fossil fuels and other human activities like deforestation and agricultural practices (NASA, 2020; IPCC, 2013). These activities have interrupted that cooling cycle by increasing the amount of carbon dioxide in our atmosphere to levels higher than they have been in at least 800,000 years (Figure 3), and will likely delay the next ice age (Stocker et al., 2013, p.37; Emanuel, 2020, p.20; NASA, 2021). If those human activities had not happened, we would currently be in a slow, steady cooling trend over thousands of years, which would eventually lead to a glacial period many more thousands of years from now. 

Why is 1 degree a big deal? What does it mean?

It most certainly does not mean that we can expect a uniform experience of any average global temperature increase in our local or regional environments. Global mean temperatures are averages over the entire globe, including land and water, and these do not reflect what that will look like or feel like at a particular time and place seasonally or otherwise (T. Murdock, personal communication, June 23, 2021). It means as global mean temperatures rise, so does the probability of extreme regional temperature anomalies, giving rise to more frequent and longer-duration heatwaves, for example (IPCC, 2013; Bush, et al., 2019). Heatwaves are generally defined as a period of consecutive days where conditions are hotter than normal for the region (Alexander, L. V., et al., 2009). 

Ok, so it gets really warm for a few days. So what? 

The impacts of a heatwave are now a lived experience for millions of people in Western Canada and the Pacific Northwestern US, and many cascading impacts haven’t necessarily even been felt yet. A few of the immediate impacts have included heat-related illness and death, an intense wildfire that decimated an entire community in less than 30 minutes, and impacts to the economy and food security from loss of crops, etc. With increasing risk of drought and heatwaves into the future, impacts from wildfires, including interface fires with communities and health impacts from smoke, and potential for severe drought leading to further crop losses are possible (Bush, et al., 2019). And that doesn’t even get into impacts to infrastructure, ecosystems, and other economic factors.

Sounds like a nightmare; so what can we do?

As discussed in Canada’s Changing Climate Report, there are opportunities to mitigate impacts through adaptation actions that will increase resilience, reduce risk and costs, and take advantage of potential opportunities for co-benefits (Bush, et al., 2019). Examples related to building resilience for heatwaves include nature-based approaches in cities that would reduce health impacts from heat, adopting adaptation measures within the forestry sector to reduce fuel loading, and increasing community preparedness and response for the inevitable increased risk during fire seasons (Bush, et al., 2019). 

The things we can control, like our behaviours and activities that contribute to GHG emissions, who we vote for, and what we support or reject as a society, could be considered our personal mitigation strategy. On the flip side, there are many things we don’t have control over, including GHGs already in the climate system and impacts that can be expected as a result, so we know we need to accept and adapt to those. The things we influence could be through a solid understanding of the likely impacts from hazards arising from climate change, and taking action to mitigate through preparedness and resilience building.

Reductions in greenhouse gas emissions are an incredibly important part of the solution to mitigate further planetary warming, and adaptation efforts will be critical to building resilience for the future warming we are already locked into. I hope that events like the heatwave of June 2021 will increase people’s awareness of the risks related to climate change so they will seek out an understanding of how to use their voice, and ultimately, create space for mitigation efforts required, and be empowered to take action on climate adaptation in their lives.

References

Alexander, L. V., and J. M. Arblaster (2009). Assessing trends in observed and modelled climate extremes over Australia in relation to future projections. International Journal of Climatology. doi:10.1002/joc.1730.

Bush, E., Gillett, N., Bonsal, B., Cohen, S., Derksen, C., Flato, G., Greenan, B., Shepherd, M., & Zhang, X. (2019). Canada’s Changing Climate Report: Executive Summary. Environment and Climate Change Canada.

Emanuel, K. (2020). Climate Science, Risk & Solutions. Massachusetts Institute of Technology. https://climateprimer.mit.edu/climate-science-risk-solutions.pdf

IPCC (2013) Climate Change 2013: The Physical Science Basis. T.F. Stocker, D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex & P.M. Midgley (Eds.), Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. 1535 pp.

NASA. (2010). How is Today’s Warming Different from the Past? https://earthobservatory.nasa.gov/features/GlobalWarming/page3.php

NASA. (2021). Climate change: how do we know?. https://climate.nasa.gov/evidence/