World Oceans Day 2: Taking the heat out of global warming

Department of Conservation —  25/05/2021

World Oceans Day is on the 8th of June. Since 1992, the United Nations has taken this day to celebrate all the ways that the ocean supports our lives and livelihoods, and to highlight the significant challenges we face in ocean conservation.

To mark this event, and key international climate change talks later this year, our marine team is bringing you a series of blogs to celebrate the vast big blue that surrounds us, while learning more about its role in climate change mitigation and adaptation. 

By Graeme Taylor, Principal Science Advisor Marine Species

Underwater canyon at entrance to sea cave, Hautapu Point Rakitu Island
📷: Dr Kim Westerskov

Last week in our first blog in this series, we discussed how the ocean regulates our climate. Now, we’re diving deeper.

The role of the ocean in regulating our climate is not without cost – we’ve been binging at an all-you-can-eat fossil fuel buffet, and so far, the ocean has been picking up the tab.

Basic physics tells us when more heat is trapped by extra carbon dioxide in the atmosphere, this extra heat has to go somewhere. To date, the ocean has absorbed over 90% of the heat we have added to our planet.

Without this, the situation would be much more dire than it already is.

For all (in)actions there’s a reaction – here are some ways the ocean has been changing in response to our oil obsession.

Crank up the thermostat

As the oceans absorb more heat from the sun, sea temperatures are rising. Nowhere is this more visible than the changes observed in the Arctic Ocean. Summer sea ice levels are diminishing in both ice thickness and size, displacing polar bears and seals.

A map showing the 2020 Arctic sea ice summer minimum. The yellow line shows the long-term median extent.
🗺: source NoAA

Ocean warming is now detectable even at depths of 2000 m.

Warming seas are observed across Aotearoa New Zealand waters, particularly in coastal areas. Effects on our native species are also becoming evident.

Rockhopper penguin colonies began declining in the 1950s on the Subantarctic islands. Now more than 95% of the breeding birds counted in the past have gone. Warmer sea temperatures and impacts on the penguins’ prey are strongly linked to this decline.

Rockhopper penguins on Campbell Island
📷: Graeme Taylor, DOC

Marine heatwaves

Marine heatwaves (and blobs) are pockets of much higher-than-average water temperatures – much like heatwaves on land.

While naturally occurring, they are becoming more frequent, longer, and more intense (again, much like heatwaves on land). How these changes will impact marine species and ocean productivity is still being studied. You can read more about this through NIWA.

Pump up the volume

As water warms, it expands. This combined with extra water from melting glaciers and icesheets is causing sea level to rise. In New Zealand, we’re currently seeing the sea rise about 2 mm per year.

Oh well, 2 mm is basically no millimeters, right? But even if we reduce our current emissions, we’re still locked into at least a 30 cm rise in sea level by 2100. It could be as high as 100 cm if our emission rates continue unchanged.

Even small sea level increases will create problems on our coastlines when storm surges coincide with spring tides.

This is a serious threat to some of our endangered seabird species that breed in coastal areas. For example, the Whenua Hou diving petrel nests in low-lying sand dunes within 20 m of the sea, and their sole breeding site covers an area smaller than two football fields. 

Diving petrel on Whenua Hou
📷: Hannah Hendricks, DOC

Here’s some food for thought: the the last time atmospheric carbon dioxide levels were as high as nowadays was about 3 million years ago. Sea levels were 15 – 25 m higher than they are today. That is the height of a six-story building!

Climate change’s ‘evil twin’

The ‘evil twin’ of ocean acidification, which is what happens when this this extra carbon dioxide dissolves in the ocean and turning it acidic, affecting creatures like paua, mussles and corals with calcium-carbonate shells.

In the last century or so, 30% of the carbon dioxide released has been absorbed by the sea, and the ocean has become about 30% more acidic.

Ocean acidification has widespread impacts – for example, it affects how well fish can hear, and the ability of organisms to produce skeletons and shells, such as coral and pāua.

More acidity even has an impact on underwater noise. Low-frequency sounds travel further in acidic waters, which may disrupt animals like whales, who rely on sound for communication, navigation, and finding food.

We can’t go back (not quickly, at least)

Humans have caused profound changes to the climate system already.

Even if we stopped emitting greenhouse gases today, global warming and changes to our oceans will continue to happen for centuries. We are really entering unprecedented territory – a massive experiment on a global scale.

But it’s not all doom-and-gloom. We can act now to minimise the scale of the damage we have set in motion.

In Part 3 next week we will discuss some of the solutions the ocean provides in our efforts to mitigate and adapt to climate change.

For more information about climate change and conservation, visit our website:

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