Climate Change
An Increase in Atmospheric Carbon
Throughout Earth's history, major changes in climate have occurred. These changes have happened along with changes in atmospheric CO2 concentration, with higher CO2 levels being correlated with higher temperatures due to the Greenhouse Effect.
Human activity has resulted in rapid increases in the amount of carbon that are more extreme than what has occurred historically, with the biggest cause being the burning of fossil fuels. Fossil fuels are carbon sinks that take millions of years to form, and their combustion releases that carbon back into the atmosphere.
How do we know how much CO2 was in the atmosphere 800,000 years ago?
You might be wondering how we can possible know how much CO2 was in the air two hundred years ago, let alone 200,000 years ago. Well, how would we determine it now? We'd collect some air and directly measure it. We do the same thing for the historic concentrations - we just measure some old air!
One of the biggest things we use to determine this are ice cores. Ice contains bubble of air - along with particles such as dust, ash, and pollen - from when the ice formed. These little pockets of air can be used to directly measure the amount of greenhouse gases that were in the atmosphere back when the bubble first formed. The same thing can happen with rocks and minerals.
Increasing Temperatures
Earth is warming.
This is not something that we are unsure of or that is being debated. The Earth is indisputably and undeniably warming.
Data comparing solar activity to global temperatures shows that the warming seen on Earth currently is not due solely to a change in solar activity. Due to the Greenhouse Effect, the rising levels of carbon dioxide in the air are resulting in an increase in global temperatures.
Global Warming, this long-term rise in Earth's average temperature, is one component of Climate Change - the changing of average conditions, including weather and temperature, of Earth.
The last eight years have been the hottest years on record. As of writing this in early 2023, global temperatures have increased by roughly 1.1°C since pre-industrial times. This change in global temperatures can have a wide variety of effects, even with what might not seem like significant increases. You can see the image to the left for a figure made by the IPCC predicting the risks associated with 1°, 1.5°, and 2° of warming.
The impacts of a warming world are wide-reaching, affecting wildlife, human health, food production, the prevalence and strength of storms, and entire human populations.
Various natural events, such as the migration of animals and the blooming of plants, are linked to changes in temperature. As these events become out of synch, animals may not be in the same area as their food sources at the same time. Migratory pollinators may not be there at the proper time to pollinate plants, aiding their reproduction. Animals may struggle to find mates.
A lot of parasites and disease vectors live in tropical areas. So much so that one of my professors from undergrad, who teaches a Parasitology course, has sworn that he will never go on a tropical vacation. As temperatures increase, their habitable zones can expand. The mosquitoes that spread malaria, ticks that spread Lyme, and fungi that infect lobsters are all spreading into new areas and infecting new hosts.
Certain reptiles and fish have a very different system for developing as male vs female than we do. Temperature-dependent sex determination results in the male/female development occurring based on what temperature was experienced during embryonic development. As temperatures increase, sex ratios are skewed. There are some islands where the vast majority of sea turtles being born are female.
As temperatures increase, soil loses moisture. Dried-out soil is more susceptible to erosion, which results in a loss of nutrients and moisture from the soil. This will result in increased difficulty for plants to establish themselves and grow, impacting wildlife and human agriculture.
As temperatures increase, ice melts. Both sea ice, such as that in the Arctic, and land ice, such as glaciers of Greenland and Antarctica, have been shrinking. This results in the loss of habitat for species that rely on the ice.
If you were to look at the ice floating in the Arctic Sea, you would notice that the ice is a bright white, while the water is a dark blue. As the ice is lighter, it has a higher albedo and reflects more light/heat. As it melts, it becomes darker, absorbing more heat and resulting in more melting - creating a positive feedback loop.
Since one positive feedback loop wasn't enough - within the tundra's permafrost lies various microbes (including methanogens), pockets of methane, and dead plant matter. As the permafrost melts, the microbes break down the plant matter, releasing methane and carbon dioxide on top of the methane that was trapped in the ice.
It is currently estimated that the Arctic will be ice-free in the summer by the middle of this century.
As glaciers and ice sheets melt, the sea level rises. Global sea levels have risen by about eight inches in the past hundred years. The rate has been accelerating, with a 4" rise since 1993. It is expected there will be an additional 1-8ft by 2100.
This is caused by two major factors: the addition of new water from the melting land ice, and seawater expansion which occurs as it warms.
This can result in displaced coastal populations, increased and more severe flooding, aquatic communities no longer being in the photic zone due to having more water above them, and coastal habitats being flooded and shifting. While this may create some new aquatic ecosystems and be a benefit for those species, it would harm those that have had their habitats destroyed.
Natural Disasters and Weather
With these increases in temperature, a wide variety of changes are expected to occur along with them. After all, it's climate change, not just temperature change.
Wildfires are expected to become more frequent and more extreme. Warmer temperatures increase the flammability of vegetation, and the amount of land affected by wildfires in the Western US is expected to increase 2-6 fold within the next twenty-five years.
Alongside increased temperatures, droughts increase the risk of wildfires. Droughts and heat waves are expected to become more intense and frequent. Areas that traditionally were drier will become even drier due to an increase in evapotranspiration due to increased temperatures, with areas that were wet possibly receiving even more precipitation. In addition, while it's easy to imagine droughts as occurring when there isn't enough rain, they can actually also happen if there's enough surface water but it all infiltrates into the groundwater too quickly. Snow melting too early in the season results in droughts becoming more likely.
If you've ever watched a hurricane map as it gets stronger and stronger, you might have noticed that they tend to increase in strength while over a warm ocean. Heat and humidity are both components of making storms stronger. Warm air can hold more moisture and also results in more evapotranspiration. As temperatures increase, there is more fuel for stronger storms. More extreme storms are becoming increasingly more common, and this trend is only expected to strengthen.
Wind patterns are determined by temperature differences. As the planet warms, temperature differences between the equator and poles decreases, resulting in weakened Hadley cells and jet streams. This results in biomes shifting, with tropical biomes expanding and subtropical areas moving toward the poles.
Thermohaline circulation redistributes heat throughout the planet via ocean currents. A major factor affecting this circulation is the wind patterns; as they change, so do the ocean currents. In addition, as land ice from places like Antarctica and Greenland melts it causes a build-up of cold freshwater near the poles, which is less dense than salt water and doesn't sink like cold water typically does. This suppresses thermohaline circulation, disrupting the redistribution of heat. Due to this, Europe is actually cooling due to climate change, rather than warming.
Effects on the Ocean
Think about a backyard (non-heated) pool. Would you rather go swimming in it after a month of 55°F temperatures or a month of 85°F temperatures?
Presumably, you chose the warmer month. Why? Because the pool water would be warmer.
As the atmospheric temperature increases, so too does the water temperature. As such, the increased emissions of greenhouse gases are resulting in a warming of our oceans. It takes a bit more energy to increase the temperature of the water than it does the air, so ocean temperatures haven't risen quite as much as global temperatures, but they have risen significantly. This can result in the loss of habitat for species, disrupted migration patterns, organisms being brought outside their range of tolerance, metabolic changes, and reproductive changes such as skewed sex ratios or disrupted mating seasons and reproductive timing.
As CO2 levels increase in the air, some of the CO2 enters the ocean via direct exchange. The CO2 combines with water to form carbonic acid, which decreases the pH of the ocean in a process known as ocean acidification. The pH of ocean water was about 8.2 prior to the Industrial Revolution and is about 8.1 now. This obviously seems like a really small difference, but as pH is based on a logarithmic scale, 1 pH is a 10-fold change in acidity.
The carbonic acid dissociates into bicarbonate ions and H+ ions. The H+ ions bind with carbonate ions present in the water. Marine organisms such as oysters rely on carbonate and calcium ions to form their calcium carbonate shells. A lack of available carbonate ions results in them being unable to form their shells and skeletons. If the pH drops too much, their shells could even start to dissolve!
One marine organism that has been especially affected by this is coral. Corals form mutualistic relationships with algae and provide a habitat for a wide number of species with their reefs.
Rising temperatures lead to stressed corals. When corals are stressed, the algae is more likely to leave the corals' tissues, which causes the coral to become bleached. Bleached coral is more susceptible to disease and loses its major food source - the algae. Some corals can recover and survive bleaching, but many die.
In addition, corals have calcium carbonate skeletons. Ocean acidification and a lack of available carbonate ions lead to more brittle corals that are less resilient.
