Visualizing Tipping Elements to Better Understand Climate Change – Part 2
Climate tipping points are a source of growing concern for scientists, policymakers, and the public. They occur when parts of the Earth system (known as tipping elements) are pushed beyond a certain warming threshold. Triggering these tipping points may lead to significant impacts, including substantial sea level rise from collapsing ice sheets, dieback of biodiverse biomes such as the Amazon rainforest, and carbon release from thawing permafrost. Therefore, it is crucial to monitor and study these tipping points and determine whether these shifts in Earth's climate system may occur rapidly or over longer periods.
In the first post of this series, we discussed what tipping elements of our planet's climate system are and grouped them into three categories: biome shift, ice melting, and circulation change. Then, we discussed tipping elements in the biome shift group in detail, how key components like the Amazon rainforest, boreal forests, and coral reefs are facing transformative changes due to global warming, and how GIS can be a useful tool in studying and monitoring these tipping elements and their impacts on our climate system. In this blog post, we will focus on the second group, ice melting tipping elements.
Map of potential ice melting tipping elements in the Earth’s climate system. Note that the marine methane hydrate deposits are hypothetical locations for visualization purposes.
Ice melting tipping elements:
Tipping elements are components of the Earth system that may respond nonlinearly to climate change by transitioning toward substantially different long-term states upon passing key warming thresholds or “tipping points". The observed shifts and changes in these tipping elements could be abrupt (less than 20 years) or rapid (several decades).
1. Loss of major ice sheets
Ice sheets are defined as large bodies of land-based ice of continental scale (> 50,000 km2). They form over thousands of years through the accumulation of compacted snow. Currently, the only ice sheets on our planet are the Greenland and Antarctic Ice Sheets, the latter being divided into the West Antarctic Ice Sheet, the East Antarctic Ice Sheet, and the Antarctic Peninsula Ice Sheet as shown in the following figure. The Antarctic Ice Sheet covers 98% of the Antarctic continent, extends over 14 million km2, and is on average 2 km deep. Read this story map collection to learn about the physical geography of the Antarctica ice sheet, and why studying and monitoring it is important. Using satellite data, researchers found that in the past two decades, Antarctica shed an average of 150 billion metric tons of ice per year.
Topography of the Antarctic ice sheet.
The Greenland Ice Sheet covers 80% of Greenland, an area of around 1.7 million km2, with an average thickness of 1.5 km. In the past two decades, Greenland lost more than 4,700 billion metric tons of ice due to surface melting and iceberg calving, an amount that is enough to cover an area of land equal to the entire United States in half a metre of water.
Greenland ice mass loss between 2002 and 2023. Areas with orange and red show a loss in ice mass whereas areas in light blue show a gain in ice mass. White indicates areas with very little to no ice mass change since 2002. Credits: NASA
In total, the volume of water held within Antarctica and Greenland would represent respectively 58 m and 7.4 m in mean global sea level rise if completely released into the world’s oceans (Source; Source). There is a high level of agreement in the scientific community on the existence of a tipping point (average temperature threshold) after which mass loss in the Greenland and Antarctica ice sheets becomes irreversible.
Besides sea level rise and its impact on our coastal cities and ecosystems, melting glaciers could result in significant biodiversity loss, as thousands of animal species are dependent on the ice pack.
Explore and learn more about sea level rise through these other resources:
- NOAA Sea Level Rise Viewer, a web mapping tool to visualize community-level impacts from coastal flooding or sea level rise (up to 10 feet above average high tides) in the U.S.
- Authoritative data sets in the Living Atlas of the World on flooding and sea level rise that are ready to be integrated into your work.
2. Permafrost Thaw
Permafrost refers to the perennially frozen soil and rock, both in the near-surface (within 3 to 4 metres) and in deeper layers of the ground, underlying a so-called active layer exposed to seasonal freeze and thaw. Approximately half of the global permafrost surface (source) is located in cold high-latitude and high-altitude areas across the Arctic, with the remaining permafrost located in parts of the Antarctic and mountainous regions in Southwest Asia, Europe and South America. In total, permafrost makes up an estimated 25% of the Northern Hemisphere and 17% of the exposed land area on Earth. Scientists estimate that it contains about 1,400 billion tons of carbon, nearly double the amount present in the atmosphere.
Geographic distribution of permafrost in the northern hemisphere.
Over the past two decades, the climate community has studied how widespread permafrost thaw would stimulate carbon dioxide and methane emissions, a potential positive climate feedback (i.e., increases initial warming) termed the permafrost carbon feedback (PCF) to climate. Alongside the global PCF and its contribution to global greenhouse gas emissions and warming, a collapse of permafrost would also pose risks to local ecosystems, local human livelihoods, health, and infrastructure. Currently, permafrost thaw poses risks to human health through the release of contaminants, such as mercury, and previously locked-in infectious diseases. Anthrax, for instance, is a zoonose disease that has been historically rare in the Arctic region but has seen recent outbreaks and extensive mortality events among humans and reindeer that have been attributed to permafrost thaw (source).
Explore and learn more about permafrost thaw through these resources:
- Rivers of Change, a story map about thawing permafrost in northwestern Canada and its potential impact on downstream environments
- The Permafrost Atlas of Canada in the Living Atlas of the World.
3. Loss of Summer Arctic Sea Ice
The shrinking of the Arctic Sea ice area through the late 20th and early 21st centuries has been documented by observations of decreasing sea ice extent in all months and all regions of the Arctic (source), especially during the summer season. Indeed, during my doctoral research in the Canadian Arctic, I personally experienced the profound effects of changes in the Arctic Sea ice, which resulted in the unexpected cancellation of our research expedition.
Arctic sea ice minimum area 1979-2022. Credits: NASA
While the loss of summer Arctic Sea ice within a couple of decades is a high-likelihood outcome under current rates of warming, a totally ice-free Arctic year-round remains unlikely outside of worst-case emissions scenarios (RCP8.5) (source). The rapid decline in sea ice extent is mainly linked to global warming that caused profound changes in the timing of melt onset and autumn freeze-up. It is also amplified by several positive feedbacks, for example, the ice-albedo feedback in which the ice starts melting, exposing a much darker ocean surface that absorbs more radiation, amplifying the warming, and then contributes to further ice loss via warming of the ocean and lower atmosphere. This ice-albedo feedback influences the global climate at large and indirectly threatens global sea-level rise by promoting additional melt from the Greenland Ice Sheet.
The loss of summer Arctic Sea ice carries significant ecological implications, as many types of wildlife in the Arctic are dependent on sea ice for shelter or survival. Changes in sea ice also pose risks in terms of food security for coastal and inland communities, as many of them are dependent on sea ice quality and season length for hunting and transportation.
Sea ice change may cause substantial shifts to phytoplankton community structure, driving transitions in regional marine ecology (source). Arctic sea ice loss also contributes to ocean acidification (lowering the ocean pH). There is robust evidence that freshwater inputs from melted sea ice increase air-sea CO2 exchanges and consequently ocean acidification.
As the Arctic will more often become ice-free during the summer, there are also concerns about associated geopolitical tensions and potential climate conflicts over access to shorter and more economic shipping routes, such as the Northwest Passage, and to offshore hydrocarbons (source).
Explore and learn more about declining sea ice through these resources:
- An Introduction to Sea Ice, a story map that takes you on a journey from the Arctic to Antarctica and introduces you to the sea ice extent on our planet, delving into its significance and the vital reasons for studying these frozen frontiers.
- Data sets in the Living Atlas of the World on sea ice extent, derived from microwave satellite data in the Arctic and Antarctic regions.
4. Outgassing of methane from marine methane hydrate deposits
Methane hydrates are white, ice-like solids formed from high methane concentrations encapsulated in water molecule cages that are stable at high pressures and low temperatures. The methane gas is primarily formed by microorganisms that live in the deep sediment layers and slowly convert organic substances to methane. These deposits occur mainly near the continental margins at water depths between 350 and 5000 metres where enough organic material is deposited in the sediments and the temperature and pressure conditions are favourable for methane to be converted to methane hydrates. In many places, gas hydrate deposits are still unexplored. However, the U.S. Geological Survey participates in national and international expeditions to study natural gas hydrate deposits and assess the amount of methane trapped in these deposits.
As sediment warming is required for methane hydrate instability, dissociation may take place on extremely long timescales of millennia, rather than over abrupt or fast timescales that would produce an acute warming spike (source). Therefore, marine methane hydrates represent a relatively lower-impact climate feedback compared to the other candidate tipping elements discussed so far in this blog post, especially for warming in the Anthropocene. If you are into ocean floor exploration like me, I am sure you will like this video of methane hydrate bubble plumes captured by the exploration Vessel (E/V) Nautilus along the west coast of North America.
Methane hydrate bubble plumes using a remotely operated vehicle (ROV) onboard the E/V Nautilus ship. Credits: EVNautilus
In the next blog post, we will discuss the final group of tipping elements, circulation change, that could potentially impact the oceanic and atmospheric circulations of our planet. We will also discuss how GIS could play a role in monitoring and studying these tipping points and what actions can be taken to prevent the Earth from crossing them.