The past two weeks have been extraordinary in the battle against global warming. Young leaders around the world have spoken out so strongly and eloquently about the importance of taking real action to address the changing climate. And millions took to the streets to support the action of youth across the world.
I am a huge fan of Greta Thunberg, the Swedish activist who has become a key figure motivating the youth movement. Her statements to Congress, the UN, and to the demonstrators were powerful and pointed. She has been in the headlines, but a diverse group of American youth have been right there leading the effort. But in addition, I have been a sailor all my life. And following her as she sailed across the Atlantic to attend the meetings in the US was a real treat of admiration and envy. How I would love such a trip!
I don’t know to what extent Greta was thinking about the impacts of climate change on the ocean as she sailed. But my guess is that she has read the science and talked to scientists about the changes that are occurring. That is what she does. And those impacts are devastating.
Changing the character of the ocean
In the polar regions and cryosphere (cold places), there are physical changes resulting from global warming. Loss of ice sheets and glaciers leads to sea level rise. The loss of snow cover increases warming because bare ground absorbs more heat. The warming of the permafrost layers with possible release of methane may accelerate warming too, as methane is a potent greenhouse gas. Loss of sea ice to levels unprecedented in the last 1000 years also amplifies warming and has the potential to influence global weather patterns. And all of these cryosphere changes affect ecosystems on land and sea.
Changes in the physics and chemistry of the ocean are dramatic and are projected to increase. Warming of the sea surface is accelerating. Currently, the ocean is absorbing and storing more than 90% of the additional heat trapped because of global warming, providing a buffer for the warming we experience on land. But that’s a lot of heat and there are consequences. Even with strong action to mitigate emissions, we have now locked in substantial increases in ocean temperatures. The same is true for ocean heat content down to 2000 m depth.
Sea level is rising and ocean pH is declining. That’s because a warm ocean takes up more volume, in addition to the added water from melting terrestrial ice sheets. And more CO2 makes the ocean waters more acidic, with consequences for sea life. Finally, there is now good evidence that ocean waters have lost oxygen content. That’s because warmer waters mix less well, and prevent re-oxygenation at the surface. Again, important consequences for marine life are predicted.
Sea life on the move
Every student learns in school that wild animals and plants are attuned to their environment. Even that simple principle tells us that as waters warm, acidify, lose oxygen and there are changes in circulation, ocean life is likely to respond. Fish and other animals that are adapted to particular temperature and seasonal patterns will move to stay within those patterns. Usually, if the water is warming that means moving poleward and deep. But that has consequences too, because each creature is part of a complex system. What if oxygen is less in deeper waters? What about other species movements? If prey and predators become disconnected, what happens? What about physical characteristics? It isn’t as if the ocean is uniform and moving poleward and deeper doesn’t come with many other changes. The new report finds that poleward shifts in marine species since the 1950’s are more than 50 km for those in the upper ocean, and nearly 30 km for those near the seafloor. Those are averages with a whole lot of variation. That means ocean ecosystems are changing in complex ways.
We depend upon sea life in many ways, from fishing to recreation to movement, to oxygen production and uptake of CO2. Nutrients are cycled in the ocean. Plant and small animals serve as the base of the food web. And humans depend upon functioning ocean ecosystems for our very lives and livelihoods. When ocean life changes, we will too.
And the report goes much farther, documenting the ongoing changes in the ocean.
Happening right now
Sometimes I hear comments that suggest that the effects of climate change are far off in the future. But this report shows that these changes are happening right here, right now. And the projections are frightening.
I grew up on the ocean. I have loved the ocean and coasts for all my life. It led me to my career in marine science. The ocean shapes where I live, the work I do, how I spend my free time, and how I think about the world. I know that change happens, but the kinds of changes this report documents are a result of careless human actions.
Greta’s generation will feel the full brunt of the climate change in the ocean. If she sails across again as an adult in 20 years, the ocean will be fundamentally different, and not in a good way. And she is right- how dare we? Her generation will never forgive us if we don’t act to address climate change.