Too Cool for Climate Change? Marine species on the brink
With the impacts of Global Warming and Climate Change becoming evermore visible in the terrestrial environment, the aquatic environment (freshwater and marine) is also struggling. Rising global temperatures and increased Carbon Dioxide (CO2) concentrations are leading to challenging conditions that many species are struggling to cope with.
Between 1880 and 2012, the global average temperature increased by +0.85 decrees Celsius. Last year, 2016 was the hottest year on record, and 2017 followed suit with another year of record high temperatures – it is set to be in the top 3 hottest years. Many would suggest the temperature increase is due to a weather phenomenon known as El Niño. This happens every few years and is caused by strong, extensive interactions between an area of the Pacific Ocean and the atmosphere. So far, 26 El Niño events have been discovered since 1900, with the strongest recorded during 1982-83, 1997-98 and 2014-16.
CO2 concentrations are up to 400 ppm (parts per million) in the atmosphere. That’s the highest its been in 3 million years. Our global carbon emissions (fossil fuel based) have increased dramatically since 1900, with 1970 increasing by 90%. 78% of emissions increase from 1970-2011 was due to fossil fuel combustion and industrial processes. Agriculture and deforestation (as well as other land-use changes) are the second highest contributors.
In some environments, even slight deviations from normal conditions can lead to catastrophic declines in survival rates. In these systems, conditions may rarely change in temperature or pH. Some habitats may be able to manage with rapid alterations regularly, while others may only temporarily have coping mechanisms, or may survive but with energetic costs, further hindering the organisms that live there.
As the air temperature of the Earth continues to increase, the oceans act like a huge heat-sink. This buffering has helped slow down rapid rises in temperature, but at what cost to the marine ecosystems? Looking at the first figure, Land Surface Air Temperature barely rises above Sea Surface Water Temperature until it reaches the year 2000. After this point, the buffering effect of the oceans seems like it cannot keep up with the rapidly increasing Air Temperature. The buffering effect appears to work best between -0.5 and 0.5 degrees Celsius. Once Air Temperature passes 0.5 degrees C, it continues to climb up past 1.0 and up to 1.5 degrees Celsius. The rapid increases of Air Temperature do not allow Water Temperature to compensate, lagging behind as temperature changes are much more subtle with water than air.
Some of the main concerns with a rise in temperature include the coldest regions as well as the more tropical areas of the planet. Warmer air temperatures lead to increased glacial activity, mainly carving (loss of ice). This is most concerning when it comes to sea level rise. Land-ice is much more of a contributor than sea-ice when it comes to sea level rise, as sea-ice displaces its volume in the water it floats on/in. If sea-ice melts, no ‘extra’ volume is added. Land-ice displaces the water only when it enters a body of water, like the ocean. Both land-ice and sea-ice have the added effect of ‘freshwater input‘ (again, land-ice more so that sea-ice, as sea-ice usually contains pockets of the concentrated brine forced out when the ice crystals form). The a main concern in the tropics is that of tropical coral. When stressed by a rise in water temperature, the corals reject their symbiotic zooxanthellae which many rely on as a main or additional food supplier. If this can occur in warm, tropical corals, then the same may also occur in cold-water corals.
Once again, the Oceans soak up what they can. However when CO2 is absorbed into water the pH is affected, becoming more acidic. This leads to Ocean Acidification. It may only seem like a small change, but to calcifying organisms this can effect the very structures they build to protect themselves. pH has already been estimated to have decreased by more than 0.1 units. That’s about a 30% increase in acidity. A further decrease of 0.3-0.5 pH units is expected by the year 2100. For calcifying organisms such as bivalves (oysters, mussels, clams), gastropods (top-shells, periwinkles, limpets), corals, and calcifying echinoderms like sea urchins. Many larger animals feed on shelled organisms, as they are lower down the food chain. Therefore if shelled organisms were to disappear, then food webs would be greatly affected.
Increasing acidity has shown to have other negative effects. Induced acidification of body fluids can have physiological and potentially reproductive issues. Reduced metabolic rates, depressed immune responses, reduced juvenile survival chances, malformations and delayed hatching times are just a few observed consequences.
Although the studies of temperature and CO2 and their effects on the ocean are still underway, it is known that both factors combined have shown the costs are greater than either could achieve alone.
Eventually, conditions may reach a ‘point of no return’, but will we be able to find a solution before then?