Dead Zones and Climate Change

Dead Zones and Climate Change

The number of dead zones has doubled every decade since the mid 1900s (Greenhalgh, 2015). The spread and increase in severity of these anoxic areas resulted from a number of factors, but future changes are expected to be heavily influence by climate change. There are several ways that climate change will impact dead zone formation and location, but temperature changes and sea level rise are the two impacts with the greatest degree of certainty.

Warmer water is able to hold less dissolved oxygen because gas solubility decreases as temperature increases, resulting in bubbles of oxygen at the surface (Greenhalgh, 2015). In addition, stratification of the ocean due to warming of the surface layer creates layers with differing temperatures and decreases the amount of mixing in the water column (Altieri and Gedan, 2014). This means the oxygen bubbles tend to sit at the surface are not distributed to deeper waters. Deep waters are also cut off from the atmosphere, a primary source of oxygen in the ocean (NSF, n.d.). These are the general trends expected as a result of warming, but all areas will not warm evenly, resulting in differing impacts in some areas. Higher latitudes are expected to see the worst dead zone changes due to warming because these areas will be experiencing the greatest overall rise in temperatures (Altieri and Gedan, 2014). Coastal areas will be impacted greater because they are shallower, and temperatures are more closely dictated by the air temperature there than the open ocean is (Altieri and Gedan, 2014).

The primary focus of sea level rise from climate change is the impact on wetland habitats. Wetlands are natural buffers to the nutrient runoff that can cause algal blooms and eventually lead to dead zones. These habitats help by filtering nitrogen and phosphorus from runoff before it reaches coastal areas (Zielinski, 2014). These ecosystems are being threatened as sea level rises (Zielinski, 2014). Declines in wetlands will result in more nutrients reaching coastal areas and contributing to algal blooms and dead zones. Sea level rise is also increasing the total volume of water susceptible to eutrophication because of the expanse in volume of shallow coastal regions (Altieri and Gedan, 2014).

There are several other less impactful and more nuanced factors of climate change that can influence algal blooms and dead zones. The first is the timing and length of algal blooms. Warming and other changes in seasonality are causing seasonal algal blooms to appear earlier into the season and stay longer, extending the period of time that eutrophication can occur and cause dead zone conditions from which the system may not be able to recover from during the off season (Altieri and Gedan, 2014). Another hypothesized impact is a hypothesis formed by a researcher named Bakun. Climate change is expected to increase the land-sea temperature imbalance in some areas due to the land heating more significantly than the ocean (Bakun et al., 2015). This would drive a greater pressure gradient in these areas that could potentially drive upwelling favorable winds resulting in greater nutrient conditions for algal growth (Bakun et al., 2015).

Climate change will also have significant impacts on ecosystem health. As temperature increases, an organism’s metabolism also increases requiring them to take in more oxygen (Altieri and Gedan, 2014). This fact, paired with an overall decline in oxygen supply, leads to worse anoxic conditions and overall lowered ecosystem resilience.


Altieri, Andrew H., and Keryn B. Gedan. “Climate Change and Dead Zones.” Global Change Biology, vol. 21, no. 4, 10 Aug. 2014, pp. 1395–1406., doi:10.1111/gcb.12754.

Bakun, A., et al. “Anticipated Effects of Climate Change on Coastal Upwelling Ecosystems.” Current Climate Change Reports, vol. 1, no. 2, 7 Mar. 2015, pp. 85–93., doi:10.1007/s40641-015-0008-4.

“Dead Zones – Special Report – SOS: Is Climate Change Suffocating Our Seas?” NSF,

Diaz, Robert J, and Rutger Rosenberg. “Spreading Dead Zones and Consequences for Marine Ecosystems.” Science , vol. 321, no. 5891, 15 Aug. 2008, pp. 926–929., doi:10.1126/science.1156401.

Du, Jiabi, et al. “Worsened Physical Condition Due to Climate Change Contributes to the Increasing Hypoxia in Chesapeake Bay.” Science of The Total Environment, vol. 630, 15 July 2018, pp. 707–717., doi:10.1016/j.scitotenv.2018.02.265.

Greenhalgh, Emily. “Climate Change Likely to Worsen U.S. and Global Dead Zones.” NOAA, 2 Feb. 2015,

Zielinski, Sarah. “Ocean Dead Zones Are Getting Worse Globally Due to Climate Change.”, Smithsonian Institution, 10 Nov. 2014,

The Climate Tipping Point

Project Team: Katelyn Boisvert, Zola Berger-Schmitz, Olivia Keck, and Matthew Heldman

Recent polls reflect increasing belief that climate change is a problem, yet it still seems few are doing anything about it. This observation results from a phenomenon we have termed the “Climate Tipping Point,” that is the point where climate awareness leads to human initiated action.

Increasing climate change awareness is an important first step; but without additional motivation to tip a person to action, we cannot make the progress needed to address this issue. There is a gap in the percentage of people who view climate change as a problem and those that believe human action is necessary to combat it, which we described as the climate action gap. Understanding how to bridge the climate action gap is necessary to positively change human behaviors related to climate mitigation and adaptation.

What drives the disconnect between climate awareness and the belief that human action is necessary to combat the climate crisis, both at the individual and at the countrywide level?

This is a question gaining traction in the world of climate research and is the focus of our research project. Many studies explore the psychological factors that contribute to this disconnect at the individual level. Whether it’s faith that technology can solve the issue, failure to comprehend the impact of an individual action, or trouble comprehending the effects of incremental changes, many individuals believe that human-initiated action to reduce the effects of climate change is unnecessary.

Climate change education and policy implementation are good ways to influence people who view climate change as a major issue and just need to take that next step toward action. Many things could prompt this step, but costs and relevance of the climate action are good motivators. It is our hypothesis that risk perception, when people feel that their life is personally at risk, is a strong driver impacting an individual’s likelihood to take action to combat climate change.

Explore this background further with our first infographic! 

There is limited research on factors contributing to the climate action gap at a countrywidelevel, so we explored several factors that could be instrumental for policy implementation.

In 2015, Pew Research Center conducted the Global Attitudes Study sampling individuals from 40 countries, which included questions on climate change. A difference in population percentage of people who said climate change is a very/somewhat serious problem and those who said human action is necessary to reduce the effects of climate change was noted worldwide, which we calculated as the climate action gap and represented geographically.

Created by Katelyn Boisvert using Piktochart Graphics

Our research compared the climate action gap for each country against factors including economics, equality, education, and risk perception to explore their potential contribution as drivers for this behavior. Economics, measured by GDP, averaged a 6% higher climate action gap for the poorest 15 countries as compared to the richest 15 countries . Equality yielded a 3% higher climate gap for countries with a higher (more unequal) Gini Index. Education did not influence the climate action gap, suggesting that climate change education may not be the determining factor in motivating individuals toward climate action.

Another PEW survey question explored if people felt they would be personally affected by climate change, which we attributed as perceived risk. This value demonstrated a positive correlation when plotted against climate action showing that countries whose residents feel more at risk from climate change are more likely to believe human action is necessary to address it, and a trend was observed for those countries as presenting with lower climate action gaps.

Curious about our results? Check out our second infographic!

Understanding the interplay of these factors is important to inform climate policy and for its success, and should focus on the need for human-initiated action and building public support for climate-friendly solutions.

Wondering about specific policy examples? Check out our last infographic!

Are you victim to the climate action gap? If so, what will push you over the tipping point? Check out our podcast on this issue! 

A list of references can be viewed