Climate change, caused by the burning of fossil fuels and the build-up of heat-trapping gases in our atmosphere, is changing the ocean in three fundamental ways:

• The ocean is getting warmer.
• The ocean is getting more acidic.
• The ocean is losing oxygen.

 

Human activities are changing our climate

When we burn fossil fuels, destroy forests or raise crops and livestock, carbon dioxide and other greenhouse gases are released into our atmosphere. These gases trap heat within our atmosphere, warming our planet.

In fact, we’ve already caused the temperature of the Earth to rise by 1.8 degrees Fahrenheit (1.0 degree Celsius) above pre-industrial levels. At the current rate, this warming is likely to reach 1.5 degrees Celsius between 2030 and 2052, and could reach 3 degrees Celsius by the end of this century, greatly impacting life on Earth. This change in our climate is also driving big changes in our ocean. 

The ocean is getting warmer 

The ocean has absorbed more than 90 percent of the extra heat caused by our greenhouse gas emissions, causing the temperature of the ocean to rise. This contributes to coral bleaching, more toxic algae blooms and disruptions to the marine food web. Warmer ocean temperatures also contribute to significant changes like extreme weather events and sea-level rise.

The ocean is getting more acidic

The ocean doesn’t just absorb heat as a result of excess carbon dioxide in the atmosphere — it also absorbs carbon dioxide itself. The Intergovernmental Panel on Climate Change (IPCC) reports that since the start of the Industrial Revolution, the ocean has absorbed about 25 percent of all of the carbon dioxide we’ve emitted by burning fossil fuels and degrading habitats that sequester carbon. This process is changing the chemistry of the ocean.

When carbon dioxide is absorbed by the ocean, it triggers chemical reactions that reduce the water’s pH — a measure of how acidic seawater is. This process is known as ocean acidification.

The ocean is already 30 percent more acidic than it was before people started burning fossil fuels. This increased acidity makes calcium carbonate molecules — the building blocks of shells, skeletons and coral reefs — harder to come by.

Animals that rely on calcium carbonate need to work harder to build and maintain strong shells — which leaves them with less energy to feed, grow and reproduce. It can also cause their shells to become thinner and more brittle. These disturbances can ripple through ocean food webs, affecting animals and ecosystems in ways scientists are just beginning to decipher.

The ocean is losing oxygen

Just like us, ocean animals need oxygen to survive. But as our planet warms, the ocean is losing oxygen and creating dead zones where nothing can live. 

As ocean water warms, it is less able to hold oxygen and becomes more stratified (which means less mixing of deep and surface waters). Warm water also ramps up the metabolism of animals and microbes, which increases their need for oxygen. All of these factors are contributing to oxygen loss in the ocean. 

Dead zones are expanding along our coasts and in the deep open ocean — sometimes covering areas thousands of miles long. Animals that once lived there may find it hard to survive and may change where they live — often moving into shallower waters. For fish that normally dive deep to avoid predators, moving to shallow waters can be dangerous.

The ocean circulates heat and moisture

The ocean is the heart of the Earth’s climate system — its currents and winds circulate heat and moisture around our planet. The weather patterns we associate with different regions of the world have been relatively stable throughout human history, thanks to the ocean.

But when the ocean absorbs excess heat — like it has over the past several decades — it can affect how the ocean circulates heat and moisture around our planet. Some regions of the world get more heat or moisture, and others get less. These changes also alter ocean currents and wind patterns, which increase the likelihood of certain extreme weather events like hurricanes, floods, droughts and wildfires.

The ocean absorbs carbon and heat

Climate change is already making our planet warmer and our weather more destructive. But without the ocean’s help, it would be much worse. To date, the ocean has absorbed more than 90 percent of the excess heat and 25 percent of the carbon dioxide we’ve produced by burning fossil fuels and degrading habitats.

Ocean and coastal habitats like coral reefs and estuaries help protect coastal communities from the impacts of storm surges and flooding. Destroying these critical ecosystems puts coastal communities at greater risk. Restoring and conserving them, on the other hand, can help us prepare for the impacts of climate change already underway.

 

Climate change causes seawater to get warmer, become more acidic and lose oxygen, which affects animals and ecosystems across the global ocean. Here are some of the most serious impacts:

Coral bleaching

Coral reefs are some of the most diverse and important habitats in the ocean. But over the last few decades, reefs worldwide have been devastated by bleaching events. Rising sea temperatures cause corals to expel their symbiotic algae — a process called coral bleaching — often resulting in the death of the coral reef. On top of warming, changing ocean chemistry (ocean acidification) is slowing the growth rate of coral reefs, with impacts throughout the food web.

Changes in growth rate, physiology, and survival

Animals are conditioned to live at certain temperatures, acidity (pH) and oxygen levels. Changes to these levels can force animals to expend more energy just to survive. This can result in slower growth, lower reproduction rates and higher vulnerability to predators.

Range shifts

Climate change is changing where ocean wildlife lives. As waters warm, many fish and invertebrate populations move toward the poles or farther offshore — seeking cooler waters. Others are getting squeezed vertically — forced to move up or down the water column as warming surface water causes low-oxygen zones to expand.

Effects on fisheries and aquaculture

The changing climate is affecting the global seafood supply and the billions of people who rely on fishing and aquaculture for nutrition and their livelihoods.

As warming waters drive wild fish into new habitats, fishermen are seeing changes in the type and amount of seafood they are able to catch. Ocean warming can also lead to smaller, skinnier fish because higher temperatures cause an increase in their metabolic rates.

As carbon levels build in the atmosphere, the resulting changes in ocean pH have resulted in high mortality of juvenile farmed shellfish. By 2100, the global annual costs of shellfish loss from ocean acidification alone could be over US $100 billion.

Toxic algae blooms

Algae are a natural and important part of ocean ecosystems. But warming ocean temperatures fuel the growth of some toxic algae faster than other species. These toxic algae blooms can harm wildlife and cause public health concerns.

In Monterey Bay and along the Pacific West Coast, abnormally warm water events (such as “The Blob” in 2015) have been linked to blooms of the algae Pseudo-nitzschia. This algae causes domoic acid poisoning, which can harm or even kill marine animals including seals, sea lions, and seabirds. In 2015, Californian crab fisheries closed due to the human health risk of eating seafood contaminated with the toxin.

 

Climate change is already negatively affecting coastal communities and economies around the world. These impacts will become more severe unless we take action to significantly reduce emissions.

Sea level rise

Over the past 100 years, global sea level has risen between seven and eight inches, on average. California’s coastal communities are already dealing with the related erosion and flooding — and experts say it will only get more severe in the coming decades. Scientists project that sea level could increase along California’s coast as much as 3 feet by the year 2100 — putting as many as 600,000 people and $150 billion in property in the state at risk of coastal flooding.

Extreme weather events

Climate change is causing more frequent and intense extreme weather events. Warmer global temperatures are contributing to record temperatures around the world, as well as to more intense droughts and wildfires. But climate change also increases the amount of moisture in the atmosphere — warmer temperatures cause more evaporation and warmer air can hold more moisture. This can inundate some regions with heavier than usual rainfall and snow, and contribute to more intense tropical storms.

Altered ecosystem services

Around the world, coastal communities rely on the ocean for food, security and tourism. Climate change is putting those services at risk. For example:

• Increased temperature and ocean acidification are affecting seafood production, threatening the livelihoods and food security of 3 billion people.
• As coral reefs degrade due to climate change, they become less able to protect coastal communities from storms. The loss of biodiversity can also negatively impact tourism.
• More extreme droughts can threaten the fresh drinking water sources that communities rely on.
• And sea level rise is exacerbating a problem called saltwater intrusion, in which overpumped groundwater aquifers become contaminated with salt.

 

Our beautiful blue backyard — the Monterey Bay — is not immune to climate change. It too is becoming warmer, more acidic and depleted of oxygen. These changes put additional stress on our local marine wildlife, from zooplankton to whales.

Monterey Bay is getting warmer

Since 1930, the surface of Monterey Bay has warmed about 1.4 degrees Fahrenheit (0.8 degrees Celsius). This warming has been linked to large blooms of toxic algae — like the one that delayed the Dungeness crab fishing season in 2015. Warming has also prompted range shifts among invertebrates, like some species of snails and anemones, that live in the rocky intertidal areas of the Monterey Bay.

Our own researchers at the Monterey Bay Aquarium have seen an increase in the number of juvenile great white sharks in Monterey Bay, and they suspect a link with climate change. Typically, these animals inhabit the warm waters of Southern California, but since 2014 they have been seen in Monterey Bay more frequently. Warming temperatures here in the bay could be a key factor bringing these sharks farther north.

Monterey Bay is getting more acidic

Over the last 20 years, carbon dioxide has built up in the surface waters of Monterey Bay — increasing the bay’s acidity by about 10 percent. MBARI scientists have been able to trace changes in Monterey Bay’s chemistry back to carbon dioxide and other pollution from traffic in Silicon Valley and agriculture in the Salinas Valley.

As Monterey Bay becomes more acidic, the marine food web and the health of our local fisheries are affected. For example, increased ocean acidity has been shown to make some juvenile rockfish slower and less energetic — which makes it harder for them to escape predators and catch prey.

Monterey Bay is losing oxygen

In addition, Monterey Bay’s oxygen minimum zone — where seawater oxygen levels are the lowest — is getting bigger. Animals that can tolerate low oxygen, like Humboldt squid, seem to be taking advantage of this development, while other animals, such as Sergestes spp. shrimp, are being displaced.

 

While climate change can seem overwhelming, the good news is that we have solutions at our fingertips to slow climate change and restore the ocean to health.

Reduce emissions

To combat climate change, we must drastically reduce human-caused emissions of carbon dioxide and other heat-trapping gases. To avoid the worst-case scenarios of impacts from climate change, scientists advise that we keep the planet’s average warming below 3.6 degrees Fahrenheit (2 degrees Celsius) from pre-industrial levels. This requires getting net carbon dioxide emissions down to zero by 2050.

How do we do that? By rapidly shifting to renewable energy — such as solar and wind — and retrofitting our energy infrastructure. The good news is we already have the technology to embrace renewable energy today.

Learn how to reduce your emissions

Reduce other threats to ocean health

To give the ocean the best chance, we must reduce other stressors it is facing. Pollution, overfishing and habitat destruction undermine the ability of the ocean to recover from changes in the climate.

We can still avoid the worst-case scenarios from climate change impacts if we drastically reduce our carbon emissions.

Preventing ocean pollution, including plastic; improving the sustainability of fisheries and aquaculture; and protecting and restoring coastal habitats, including wetlands, can help make the ocean more resilient in the face of climate change.

Support climate policies

Local, state and global leaders are creating policies designed to reduce greenhouse gas emissions and protect ocean habitats and communities from the impacts of climate change.

Paris Agreement

The Paris Agreement is the first global commitment by world leaders to fight climate change. Signed in 2015, the Paris Agreement set the goal of keeping the average global temperature within 2 degrees Celsius of pre-industrial levels. The Agreement called on each nation to set its own targets and strategies to reduce emissions.

State and local policies

State leadership is critical in combating climate change. In our home state of California, leaders have set ambitious targets to reduce emissions and to transition the state to renewable energy over the next few decades. This could include expanding existing forms of renewable energy, such as solar and land-based wind energy, and exploring potential new sources of renewable energy like offshore wind.

California agencies, including the Ocean Protection Council, are taking measures to protect the overall health of California’s coast, including through a system of marine protected areas.

Regional governments and businesses can take action by reducing their energy use, sourcing renewable power and helping their communities prepare for changes already underway.

Read the Ocean Climate Action Agenda

Protect and restore critical ecosystems

Some coastal habitats help reduce the impacts of climate change by taking carbon dioxide out of the atmosphere. Mangroves, seagrasses and wetlands — sometimes called “blue carbon” ecosystems — act as carbon sinks, absorbing carbon dioxide and storing it below ground.

Protecting and restoring blue carbon ecosystems — and the critical services they provide, from seafood production to coastal protection — is an important climate solution.