Costly Climate Change and Marine Cleaning

Dr Anjani Ganase looks at some of the latest marine and climate science research.

 

 

The World Meteorological Office reported a seven-fold increase in extreme events since 1970s. While some of the increase is associated with better reporting mechanisms and population expansion, climate change is a major driver. Given the projected increase in extreme climate events, researchers from New Zealand have assessed the global cost of extreme events attributed to climate change over the last twenty years. Assessments pertaining to the US alone estimated a cost of $260. 8 billion in economic damages related to climate change, which roughly made up 53 % of the total cost. Most of the cost was associated with storm damage (64 %), followed by heat waves (16 %), then flood (10 %) and drought (10 %), wildfires (2 %) and cold events (2 %).

 

Over the last twenty years, the extreme events that cost the most in the US were the storm events of 2005 – Katrina, Rita and Wilma ($123 billion in damages) - and then 2017 – hurricanes Harvey, Irma and Maria ($139 billion).  Extrapolation to the global cost totalled about US$ 2.86 trillion, or US$ 143 billion/ year. The largest component of this cost is loss of life, which comprised 63% or 90 billion dollars annually, while economic damages were $53 billion annually. Other extreme events that contributed to the global cost of damages varied from the US assessment. The years of greatest loss were 2003 – European heatwave (55,400 deaths associated to climate change); 2008 – tropical cyclone Nargis in Myanmar; and in 2010, heat waves in Russia and drought in Somalia.

 

The results reveal the need for the implementation of climate change adaptation strategies, especially to reduce loss of life. The study suggested some examples, such as the development of a heat wave warning system, shifting hours of operation and public access to cool areas. Some of these were applied in France after the 2003 heat wave, with fewer casualties even when more severe heat conditions were experienced. In the Caribbean, infrastructure policies for buildings capable of withstanding extreme storms are needed along with better disaster preparedness.

 

Humpback whales, Reunion Island. Credit: François Baelen / Ocean Image Bank

 

Marine heat waves in the deep oceans

 

Since the 1980s, surface sea temperatures of the ocean have been monitored remotely via satellites. Where warming events develop and overlap with ecosystems of significant biodiversity such as coral reefs, countries can receive warming alerts from NOAA. Today, the Caribbean, including Trinidad and Tobago, are experiencing one of the most severe heat waves in 15 years resulting in mass coral bleaching. More frequent and severe marine heat waves (MHW) are expected in the future because of climate change. Scientists have re-analysed marine heat waves data over the last 25 years specifically assessing the patterns of MHW with depth. While ocean surfaces (0 -50 m depth) experience a higher frequency of heat waves, the subsurface marine heat waves between 50 – 200 m may be more intense and can last twice as long. Meanwhile heat waves in the very deep areas (~2000 m), while less severe compared to the surface may still be detrimental to the deep-sea biota, given their sensitivity to physical changes.

 

The impact of sub-surface marine heatwaves is expected to be more harmful in areas that house higher marine biodiversity, such as in tropical and polar areas, and especially among species that exist in environments close to the thermal tolerance thresholds, such as mesophotic reefs. The presence of these sub-surface marine heat waves is likely to result in die off and redistribution of marine biodiversity. Geographically, the most intense marine heat waves are expected in the equatorial regions at depths around 100 m, while the polar regions will experience the longest duration of marine heatwaves. Approximately 14 % of the ocean have areas of high biodiversity with high intensity heat waves down to 250 m. Locations include the Philippines, Tasman Seas (west Pacific), The Gulf of Mexico and off South Africa. While surface heat waves can be detected by satellites, sub-surface heat waves are not so easily detected, and sub-surface temperature rise is likely to become more frequent because of climate change.

 

 

Male whales in the post whaling era

 

Since the banning of whaling in in the 1960s when whale populations were at the brink of extinction, most of the populations around eastern Australia have bounced back to pre-whaling numbers with over 20,000 whales. Considering that most whales live up to 60 + years, it is the first time that scientists are able to observe large groups of adults. Scientists have observed changes to whale populations and behaviour in the post-whaling world. One interesting observation is that as male population densities increased over the years, changes in mating behaviour have also occurred. In early years, when whale populations were low, male whales would sing to attract females. As densities increased, males engage in more physical courting tactics.

 

Singing was often conducted by a lone male or a male in a group of two or three. As groups increased to four or more males or where more than one male sang, the competition would often shift to a physical one where the males would block other males while escorting a female. Scientists believed that the change in behaviour was to prevent competition by other males. The ability of males to change tactics when courting females is seen as a sign of evolutionary variability and adaptability in whale populations and a sign of success for recovering populations.

 

Discarded fishing gear in Canada

 

Fishing gear – lost, abandoned, or intentionally disposed - can cause significant harm to marine life. Ghost nets can drift hundreds of kilometres in the mid water column entrapping and drowning marine mammals and turtles. Fish traps continue to entrap fish, crabs and lobsters for years after being abandoned. When nets and lines end up on reefs or the seafloor, they smother the benthic community and entangle fauna. An effort to remove all abandoned or lost fishing gear was conducted in southwest Nova Scotia, Canada in 2020.  A partnership among government, academia, fisherfolk and NGOs was mounted to locate and retrieve abandoned fishing gear which largely comprised lobster traps as the major commercial fishery in the area.

 

Annually about 2% of lobster traps are lost in southwest Nova Scotia. Locating and retrieving lost gear is logistically difficult and expensive. To determine where should be cleaned up, meetings with fisherfolks were done to identify areas of higher gear loss. This was then meshed with the fish and lobster habitats to assess the level of risk to indigenous marine life. Just under 4,000 km of seafloor were covered while conducting 997 tows over two years. Grapples, while not the perfect tool, were able to retrieve ~29,298 kg of fishing gear from the seafloor, while 4,668 kg of abandoned fishing gear were also retrieved from the coastal areas. Majority of the fishing gear consisted of fish traps; the oldest being 37 years, and many with entrapped creatures. About 25 species were released, with the largest proportion of by-catch being American lobster (48 %), followed by commercial crab species.

 

With respect to the gear technology, new traps were more efficient at entrapping marine life but some of the newer traps also had escape panels. The escape panels had attachment rings that would disintegrate and release by-catch. Some panels had fallen off and had less by-catch but many of the panels were still intact. More research is needed to determine the length of time these take to disintegrate.

 

References

Dunlop R, Frere C. Post-whaling shift in mating tactics in male humpback whales. Commun Biol. 2023 Feb 16;6(1):162. doi: 10.1038/s42003-023-04509-7. PMID: 36797323; PMCID: PMC9935900.

 

Fragkopoulou, E., Sen Gupta, A., Costello, M.J. et al. Marine biodiversity exposed to prolonged and intense subsurface heatwaves. Nat. Clim. Chang. 13, 1114–1121 (2023). https://doi.org/10.1038/s41558-023-01790-6

 

McIntyre, J., Duncan, K., Fulton, L., Smith, A., Goodman, A. J., Brown, C. J., & Walker, T. R. (2023). Environmental and economic impacts of retrieved abandoned, lost, and discarded fishing gear in Southwest Nova Scotia, Canada. Marine Pollution Bulletin, 192, 115013.

 

Newman, R., Noy, I. The global costs of extreme weather that are attributable to climate change. Nat Commun 14, 6103 (2023). https://doi.org/10.1038/s41467-023-41888-1