Global Climate Change

The Consensus Is Clear

Research on climate change is extensive (see chart below) with over 234,823 publications from researchers all over the world. All major scientific and government research organizations agree that climate change is occurring, it is caused by human activity, and it poses grave dangers for natural and human systems. I will summarize our current understanding of climate change in this and the next lectures. If you want to do the research for yourself, you can visit:

A Quick Review of Climate

Climate is a region's general weather pattern. Some important components of climate are temperature, rainfall, and seasonality.

Climate change includes changes in temperature, rainfall, and seasonality patterns. This is significant because so many phenomena in nature are affected by these variables: species distributions, distributions of biomes, primary productivity, decomposition, etc. We have seen the importance of these variables again and again throughout this class. Although average planetary temperatures are increasing, climate change does not mean everywhere is getting warmer and dryer. Some areas will get warmer, some areas will get cooler, some areas will get wetter, some areas will get dryer, but everywhere on the planet will be affected by climate change and species and ecosystems will be affected.

The Greenhouse Effect

The greenhouse effect is a natural process that keeps the planet warmer than outer space and, therefore, allows life on the planet to persist. It is not a problem in and of itself, but it is the mechanism through which humans have been causing climate change. What happens is that the sun’s energy enters the atmosphere (the envelope of gasses that surrounds the earth) as intense high energy light (near-infrared wavelengths) that passes easily through the atmosphere and heats the earth’s surface. This lower intensity longer wavelength heat energy is released form the earth’s surface into the atmosphere where it becomes trapped by greenhouse gasses (Carbon Dioxide, Methane, Nitrous Oxide, and Halocarbons).

Each molecule of these greenhouse gasses can hold on to a specific amount of heat based on its chemical formula. The larger the number of molecules of these greenhouse gasses in the atmosphere, the more heat is held in the planetary system. A temperature balance is reached between what comes into the planetary system and what leaves the system after all of the molecules of these gasses have become saturated with the total amount of heat that they can hold.

Through burning Fossil Fuels (Coal, Oil, and Natural Gas), Agriculture, and Deforestation, humans have increased the concentrations of these gasses in the atmosphere, resulting in more heat being held in the system, and the average temperature of the atmosphere, oceans, and land warming up. The increases in greenhouse gas concentrations are:

CO2 - Carbon dioxide (Multiple Human Contributors)
- Increased by 41% since pre-industrial times from 280ppm to 414ppm
CH4 – Methane (Agriculture and Fossil Fuels)
- Increased 151% since pre-industrial times
N2O - Nitrous oxide (Agriculture)
- Increased 20% since pre-industrial times
Halocarbons do not exist naturally, but were created by human chemists, therefore, we do not have pre-industrial numbers, but concentrations in the atmosphere have continued to increase since their creation.

Carbon dioxide has the highest concentration in the atmosphere of any of these gasses. It is the largest contributor to global climate change. As long as humans continue to increase the concentrations of these gasses in the atmosphere, average planetary temperatures will continue to increase. The faster we release these gasses and the higher the concentrations get, the faster the planet warms and the greater the total amount of warming. It takes time for the concentration of these gasses in the atmosphere to reach their saturation level. If we stopped producing greenhouse gasses today, the planet would continue to warm until all the gasses we have already released become saturated with the total amount of heat that they can hold. The planet would then reach a new equilibrium temperature, but it would be higher than in the past because the concentrations of these gasses are higher than they were in the past. In 1850, CO2 concentration in the atmosphere was 280 ppm (280 molecules of carbon dioxide for every million molecules in the atmosphere), but today CO2 concentration is over 414 ppm.

The concentrations of these greenhouse gasses are the highest they have been in at least 800,000 years. We know this because we can collect data on past greenhouse gas concentrations and temperatures using ice cores from glaciers (see graphs below).

What we see when we look at climate using ice cores and other techniques, including direct measurements, is that the concentrations of all of these greenhouse gasses skyrocketed following the industrial revolution when we started burning fossil fuels to run our society. This is another consequence of the growing human population, the increase in average resource use per person, and advancements in technology (I=PxAxT).

We know these increases are a product of human activities, because we can trace their signatures to their sources, and we can measure emissions at the sources. Human generated greenhouse gasses come from the following sources:

We know which countries are the highest emitters of greenhouse gasses. China and the U.S. are the number 1 and 2 emitters of greenhouse gasses (see below):

Current Evidence of Global Climate Change

We can measure a host of changes that have occurred on the planet as a result of greenhouse gas emissions we’ve released so far. Average global temperatures increased by 1oC (1.8oF) between 1901 and 2016. The pattern in this temperature shows the rate of warming is increasing. Each of the last 3 decades were successively warmer than any since 1850 and the 17 warmest years on record having all occurred since 1998. The graph below (left), shows deviations in temperature from the 1961 to 1990 average (the horizontal black line). The graph below (right), shows decadal temperature averages relative to the 1961 to 1990 average (0.0 on the graph).

A 1oC rise in average global temperatures may not seem like much to us, but the planet is telling us that this amount of warming over this time frame is significant. We’ve seen the following measurable effects of this 1oC rise in temperature:

Weather patterns have changed resulting in more and bigger fires (like we’ve seen in California and Australia), drought, beetle kill of trees (throughout the Western United States and Canada), and more severe storms and flooding (as seen in Florida and Texas).
Many terrestrial, freshwater, and marine species have shifted their geographic ranges, seasonal activities, migration patterns, abundances, and species interactions.
An analysis of data for over 2000 responses by animal and plant species showed that species are moving up in elevation at a rate of 12.2 meters per decade and toward the poles in latitude at 17.6 kilometers per decade.
Sea levels rose 0.19m (7.4 in) between 1901 and 2010.
Global snow and ice extent has decreased.

Comparison of Arctic Sea Ice in Summer 1984 to 2016

Melting of Upsala Glacier, Argentina Between 1928 and 2004

Watch This Video of a Glacier Retreating

(Music only. No narration.)

Predicted Climate Changes and Consequences

We use computer models to extrapolate into the future what the effects of climate change will be. How much the planet warms, and the impacts of that warming, depends on the choices humans make. Will we continue on with business as usual or will we aggressively reduce fossil fuel use and other sources of greenhouse gas emissions?

The Intergovernmental Panel on Climate Change (IPCC) predicts 0.3°C to 4.8°C warming this century (2081-2100 average verses 1986-2005 average) while the U.S. Environmental Protection Agency (EPA) estimates 2 to 4.5oC (2.6 to 8.1oF) is the most likely outcome by 2100.

The Paris Climate Accord from 2015 codifies the voluntary pledges of the world’s nations to address climate change. The world’s nations are not on track to meet these goals, but even if they were, temperatures would rise 3oC by the end of the century.

The IPCC estimates we need to keep total warming below 1.5oC to prevent catastrophic changes on the planet. For instance, at 1.5oC as much as 30% of the world’s coral reefs may survive until 2050. With 2oC warming less than 1% of the world’s coral reefs are likely to survive until 2050. Another concern about warming more than 1.5oC is that carbon, stored in permafrost in the arctic and other locations, could be released compounding what’s been added by humans.

To put predicted warming in context:

Warming of 1oC per century would be faster than any warming in the last 10,000 years. We are on track to warm 3 to 4 times this rate.
For every 1oC rise in temperature, scientists estimate that climate belts (temperature and rainfall patterns found at different latitudes) will shift 100-150 km in mid-latitudes and altitudinal belts will increase150 m in altitude. This means a species adapted to live in Orange County today would need to be able to colonize and take up residence around San Louis Obispo by the end of the century. Remember the ability of a species to migrate depends on their dispersal ability, barriers they have to cross, and the distance of those barriers. How many species can move this far in less than 100 years across a landscape altered by human activities? Scientists estimate a large percentage of the world’s species will not be able to make these migrations at the rate they would need to.
- Scientists estimate that 1 million species will go extinct this century from climate change alone without significant mitigation of greenhouse gas emissions.

Other predictions are:

Global sea levels will rise between 1 and 4.3 feet (globalchange.gov) this century. A common estimate is around 3 feet of sea level rise by 2100.
The arctic will be nearly sea ice free in summers by 2040 (globalchange.gov).

Watch This Video on Natural Factors That Affect Earth’s Climate

Past Warming Events Inform Our Understanding of Climate Change

Watch This Video on Warming Events in the Planet’s Past

Ocean Warming, Ocean Acidification, and the Future of Corals

The graph above shows the rising emissions of greenhouse gasses from human activities above the 0 line. Below the 0 line, it shows where in the environment those gasses have accumulated. About 46% of the emissions have accumulated in the atmosphere; about 26% have accumulated in the oceans; and about 28% have been absorbed by plants.

The 46% that has accumulated in the atmosphere is what is holding on to the heat that results in global climate change. In a sense, it is good that not all of the emissions have accumulated in the atmosphere, because if they had, the amount and rate of warming would be much greater than it is. However, the CO2 that has been absorbed into the oceans results in another environmental problem called ocean acidification.

The rising temperatures and ocean acidification both have severe impacts on marine systems. 93% of the excess heat that has resulted from human released greenhouse gasses since 1970 has accumulated in the oceans. The upper 75m of the ocean warmed by 0.11oC per decade over the period 1971-2010. By 2100, it is likely that ocean temperatures will increase 1-4oC. This will likely result in an ocean net primary production (total energy capture in the oceans) decrease of 3-10%, fish biomass decrease of 3-25%, and the total loss of coral reef ecosystems.

Remember, coral reefs are formed by coral polyps that have a mutualistic relationship with zooxanthellae algae that live inside their tissues:

The corals provide shelter for the algae and products that the algae need for growth, such as CO2, nitrogen, and phosphorous produced as waste products from the corals. In exchange, the algae provide the products of photosynthesis for use by the corals, including oxygen, glucose, and amino acids, and absorb wastes produced by the corals. The corals use the materials provided by the algae to build proteins, fats, carbohydrates, and their calcium carbonate shells. Zooxanthellae produce almost 90% of the energy used by corals, so without their mutualist symbiont, corals would eventually starve.

The coral polyps build hard shells out of calcium carbonate (CaCO3) in which they can take refuge. The corals extend these shells as they grow, and when a polyp dies, a new polyp builds its shell on top of the shell of the dead polyp. Overtime, the dead "skeletal" material of generations of corals build up on top of each other forming the structure of the coral reef. The current generation of polyps forms a thin living layer around the built up calcium carbonate shells of past generations.

One major consequence we see from ocean warming is coral bleaching. The group of corals that build coral reefs (hexacorals) have a narrow thermal tolerance. They only grow in the warm waters of the world, but if the waters get too warm the temperatures can exceed corals’ thermal tolerances. When this happens, the mutualism between corals and their Zooxanthellae breaks down. The corals eject the algae (which give them their color). We can then look though the clear body of the coral polyp, and see the white skeletal material beneath. We call this process coral bleaching. If the waters stay warm too long (around 3 weeks), the corals die because they are not getting the products from their algae mutualist that they need to survive.

Watch This Video on Coral Bleaching

In 2020, the Great Barrier Reef in Australia, the largest barrier reef in the world, experienced its third major bleaching event in five years. The 2016 bleaching event in the great barrier reef resulted in the death of 22% of the reefs corals. In the Caribbean on the Mesoamerican Reef, the second largest barrier reef in the world, live coral cover has declined from 50% to 8% in 50 years (overfishing has also contributed to this). In total, over 25% of the world’s live coral cover has been lost in the last three decades.

Ocean warming is having a significant impact on marine species, but it is not the only consequence of human generated greenhouse gasses for the marine environment. Ocean Acidification is also a significant problem. The 26% of CO2 that gets absorbed into the ocean goes through a series of chemical reactions that change the PH of the ocean. This reduces the availability of carbonate ions that corals (and other organisms) use to build their calcium carbonate shells. As a result, corals grow more slowly and less densely. Eventually, the rate of coral growth cannot exceed the rate of erosion by physical and biological activities, and the reef declines.

Watch This Video on Ocean Acidification

Ocean surface acidity has increased 30% from CO2 released by humans. This rate of acidification seems unparalleled in at least the last 66 million years (globalchange.gov). By 2050, ocean acidification is expected to reduce calcium carbonate saturation rates to marginal at best for coral reefs throughout the world’s oceans. See the graph below: Pre-industrial Locations of Coral Reefs Are Shown in Blue.

The pictures below show the effects of coral bleaching and ocean acidification:

Scientists estimate that for coral reefs the safe level of CO2 in the atmosphere is 320-350ppm. We have already exceeded this with over 414 ppm CO2 in the atmosphere. 33% of reef building coral species are currently threatened with extinction and less than < 1% of the world’s coral cover is expected to survive until 2050. This is significant. Although coral reefs cover less than 0.1% of the sea floor area of the world’s oceans, they provide habitat for over 25% of marine fish species. More than 500 million people depend on coral reefs for food, income, and coastal protection. Coral reefs provide ~ $9.8 trillion globally of social, economic, and cultural services each year. We lose these benefits if we lose coral reefs.

What Can We Do About Climate Change

Scientists are very concerned about the consequences of climate change and ocean acidification because it is contributing to a variety of environmental and human problems (increasing the rate of extinction, contributing to ecosystem collapses, resulting in 2 billion climate change refugees by 2100) and is expected to continue to get worse unless we take significant action immediately. We have seen from our examination of the fossil record that over geological time, warming, acidification, and ocean anoxia (lack of oxygen in ocean waters resulting from warming waters and nutrient pollution) are linked with major extinction events. There are a variety of actions that we can take to reduce warming, but recent reports indicate that we only have about 10 years to act aggressively if we want to head off the worst consequences of global warming and ocean acidification. If average global temperatures reach 2oC, less than 1% of the world’s coral cover will survive, but if we warm no more than 1.5oC, 10-30% of the worlds coral cover could survive.

How Do We Address Climate Change and Ocean Acidification?

Discontinue use of fossil fuels by replacing human energy supply with non-carbon emitting sources. We need to cut human generated greenhouse gasses by 45% below 2010 levels by 2030 and reach 0 human generated greenhouse gas emissions by 2050. There are many alternatives to fossil fuels we can aggressively pursue. Many of them have their own impacts, but we have to weight these against the impact of climate change. Non-carbon emitting sources of energy include solar, wind, hydro, geothermal, tidal, etc. Part of the reduction in greenhouse gas emissions can also be met by increasing energy efficiency so we don’t need to produce as much energy.
Reduce habitat destruction. Growing vegetation absorbs and sequesters CO2 into the structure of plants. When vegetation is removed and decays, it releases CO2. Habitat restoration will increase the amount of vegetation absorbing CO2.
Slow human population growth. More people use more energy, produce more greenhouse gasses, and cause more habitat destruction (I=PxAxT).

Unfortunately, we are not on track to meet these goals. Between 2015 and 2040, world energy consumption is predicted to grow 28%, and CO2 emissions from energy production are expected to increase 16%. By 2040, fossil fuels are still expected to provide almost 77% of world energy (US Energy Information Administration’s International Energy Outlook from 2017).