"Plastics now pollute all dimensions of our ocean from the sea surface to the seafloor, on remote beaches and in Arctic sea ice."
Nick Mallos, Trash Free Seas®
WHAT IS THE EVIDENCE FOR CLIMATE CHANGE?
Graph showing carbon dioxide levels (ppm) over the past 800,000 years showing that atmospheric carbon dioxide levels have dramatically and rapidly increased since the industrial revolution when compared to past climate measurements. (Credit: Luthi, D., et al.. 2008; Etheridge, D.M., et al. 2010; Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa CO2 record.)
There is a vast amount of evidence that leads to the conclusion that we are experiencing rapid changes to our global climate, and it is more than just increasing surface temperatures. We are also witnessing changes in the atmosphere, ocean, cryosphere, and biosphere. Since the 19th century, we have recorded increases in global average sea temperature, warming in the troposphere (the lowest 6-10 km of the atmosphere), increases in precipitation over land, increases in the acidity of the ocean, decreases in Arctic sea ice area and thickness and extent, increase in sea level, shifting of the range of some species, plants are blooming earlier in the spring, and much more. There is overwhelming evidence from a broad range of disciplines using a broad range of techniques that we are in a climate system that has experienced rapid warming since the industrial revolution.
Graph from NOAA NCEI, where the red and blue bars show yearly temperature compared to the twentieth-century average, and the grey line shows atmospheric carbon dioxide concentrations. Original graph by Dr. Howard Diamond (NOAA ARL), and adapted by NOAA Climate.gov.
HOW IS THE CURRENT WARMING ANY DIFFERENT FROM EARTH'S WARMING IN THE PAST?
Throughout Earth’s history, the climate has always varied naturally, but there are two key differences between the current warming and the temperature variations in the past: it is warming rapidly and it is warming almost everywhere. We know that there were times in Earth’s past when the temperature fluctuated from paleorecords from ocean and lake sediments, glaciers, and tree rings. The warming period that we are currently experiencing has reversed a slow, long-term cooling trend and research shows that the global surface temperature is the highest it has been for millennia.
During the 5000 years that it took to shift from the last glacial period to the current interglacial period, the global temperature increase was about 5°C, with a maximum warming rate of about 1.5°C per thousand years. To compare, Earth’s surface warmed roughly 1.1°C from 1850–1900.
The rate of global warming during the last 50 years has exceeded the rate of any other 50-year period for the past 2000 years. In short, Earth’s previous temperature variations were caused by large-scale natural processes, while the warming we are currently experiencing is predominantly due to human causes.
In short, natural processes without human activities would push our planet into a cooling period.
Graphic modified from the Intergovernmental Panel on Climate Change. Many aspects of the climate have reached unprecedented levels due to human activity in at least the past 2000 years. (IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change).
Human-caused greenhouse gas emissions cause the temperature of the Earth’s atmosphere to increase. This temperature increase will warm the poles and the ocean, which means a hotter planet will also include rising sea levels. As the ocean warms, the ocean’s oxygen level will decrease, killing coral reefs and causing phytoplankton (the base of marine food chains) to decrease and affect all other marine life.
A hotter planet will come with increasingly more climate disasters happening simultaneously, such as hurricanes, wildfires, and severe rains that cause flooding. In the 1980s, there were an average of 4 billion-dollar disasters caused by extreme weather every year. That figure has tripled in the last 5 years; we now average 12 billion-dollar disasters caused by extreme weather each year (these damage totals are adjusted for inflation). This increase in extreme weather happened as the planet has warmed just under 2 degrees Fahrenheit since the late 19th century. The planet is projected to warm another 2 degrees by 2100, and even more if nations fail to cut their greenhouse gas emissions. All impacts of climate change will only become more severe if we don’t act immediately to stop greenhouse gas emissions.
WHAT DOES A HOTTER PLANET MEAN FOR OUR FUTURE?
HOW DO WE KNOW HUMANS ARE RESPONSIBLE FOR CLIMATE CHANGE?
Natural fluctuations in the Earth’s climate are caused by a variety of phenomena. Variations in solar activity, large volcanic eruptions, climate cycles such as El Niño, wildfires, and more can all cause the short and long-term climate to fluctuate. Variations in solar activity alter the amount of energy we receive from the sun and have made little difference in global temperature in the last century. Volcanic activity actually has had a global cooling effect that lasts for several years due to an increase of aerosols in the upper atmosphere that reflects sunlight. Neither of these processes is enough to explain the rapid, global warming we are experiencing.
The major human contributors to climate change are burning fossil fuels, which increases the concentrations of greenhouse gases and aerosols in the atmosphere, and deforestation, since forests are one of the major carbon sinks on Earth, and chopping down trees releases these greenhouse gases into the atmosphere. Greenhouse gases trap the Sun’s heat (infrared radiation) close to the earth’s surface. Aerosols, such as those produced by natural volcanism, help to cool the climate by increasing sunlight reflection. Decades of evidence show that human contributions are the primary cause of recent climate change. The current concentrations of major greenhouse gases (carbon dioxide, methane, and nitrous oxide) in the atmosphere are unprecedented in at least the last 800,000 years.
Graph from NASA showing the total energy that the Earth receives from the Sun in watts (yellow line) and global surface temperature changes (red line) from 1880 to 2020. The solar irradiance (the energy we receive from the Sun) shows a decline since the late 1970's, so it doesn't seem likely that the Sun is responsible for the global warming we have experienced for the past several decades. (Credit: NASA/JPL-Caltech)
HOW IS CLIMATE CHANGE AFFECTING ANIMALS?
The warming climate affects animals both directly and indirectly. Animals are indirectly affected because the warming climate changes ecosystems, limiting many species’ range of hospitable habitats, as well as disrupting the food chain, and limiting successful reproduction. In polar regions, animals that live on ice are struggling to survive as polar ice melts. In North America, moose are struggling due to an increase in ticks and parasites and their ability to survive longer in the shorter and milder winters. Salmon are struggling to survive as climate change causes the temperature to increase and change the flow of waterways because they rely on cold, steady-flowing rivers to spawn, and this, in turn, affects the animals that depend on salmon for food, such as orcas and grizzly bears. On the other hand, some species will flourish in a warmer climate, but this isn’t necessarily a good thing. In the words of NPS, “not all wildlife belong where they flourish.” These species will expand their hospitable habitat ranges and food source and become invasive species, outcompeting native species of both plants and animals, and eventually destroy these environments due to the invasive species having no natural predators in their new habitat.
HOW IS CLIMATE CHANGE AFFECTING PEOPLE?
Climate change is affecting people around the world in innumerable ways. It has brought about potentially irreversible changes to all of Earth’s major systems that have led to large-scale environmental hazards. It is changing weather patterns, causing extreme weather, increased wildfires, stress on agriculture and means of producing food, loss of biodiversity, forcing displacement, destroying homes and communities, and much more. The impacts of climate change disproportionately affect marginalized and low-income communities first and most severely because they are much more vulnerable to environmental hazards and generally live closer to the biggest polluters, such as factories and mines, and have the least resources to prepare for and respond to health threats, even though they have contributed to greenhouse gas emissions far less.
Graphic from NOAA showing groups of people that are at higher risk of exposure to climate-related environmental health hazards. (EPA (National Climate Assessment)).
HOW IS CLIMATE CHANGE AFFECTING THE OCEAN?
Since the 19th century, scientists have recorded changes in the world’s oceans that indicate that both the Earth and the Earth’s oceans are warming. These changes include average sea surface temperature increasing globally, relative acidity of the ocean increasing (the rate of ocean acidification is higher than it has been in 300 million years!), melting polar ice, shifting ocean currents, coral bleaching, fish migrations, and more. Natural carbon sinks such as forests, soils, and oceans have absorbed about half of the carbon dioxide that has been emitted due to human activities, slowing the rate of climate change. Furthermore, more than 90% of excess energy in the world’s climate system is being stored by the ocean, causing the heat content of the ocean to increase globally since the 19th century. The Earth’s natural carbon sinks do have a limit, though, and observations show that they are beginning to respond to increasing levels of carbon dioxide in the atmosphere, meaning that continued warming will weaken nature’s ability to take up excess carbon dioxide over time, and ultimately lead to increasing climate change and global warming.
The warming effect has caused ocean waters to expand and contribute to rising sea levels in the past century, along with melting polar ice, and has caused ocean currents and fish migrations to shift, and has led to coral bleaching/die off. The rising acidity of the ocean has negatively affected many marine animals and habitats but is particularly harmful to shellfish who have trouble growing shells as water becomes more acidic. The shifting ocean currents cause a much deeper issue; they affect the ability of the ocean to mix with deep, nutrient-rich waters and in turn limits the growth of phytoplankton, which affects the whole food chain.
Graphic from Monterey Bay Aquarium Research Institute showing the threat of climate change on the world's oceans, including increasing ocean temperature, ocean acidification, decreasing oxygen, higher sea level, ad more intense tropical storms (IPCC, 2019: Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC)).
HOW IS CLIMATE CHANGE AFFECTING RAINFORESTS?
Rainforests are critically important. They produce most of the oxygen we breathe, and although rainforests make up less than 2% of Earth’s total surface area, they provide habitat for half of the world’s plants and animals. The Amazon rainforest alone contains ~10% of the world’s known species. In addition, the Nature Conservancy states that 70% of the plants identified by the U.S. National Cancer Institute as useful in the treatment of cancer are found only in rainforests.
Like oceans, rainforests are one of Earth’s natural carbon sinks but unfortunately, they are being cut down at an alarming rate and releasing more than 1.5 billion tons of carbon dioxide into the atmosphere. For scale, that is roughly 15% of all human-caused carbon emissions. Once rainforests are degraded to their tipping point, they will lose their ability to produce their own rainfall, and gradually turn into a dry savanna. Studies of the Amazon river basin show that a warming climate comes with a 10-20% decrease in rainfall, as well as an increase in wildfires. Deforestation also leads to food shortages for both wildlife and the millions of people that depend on rainforests to survive.
Graph from Statista showing the estimated yearly carbon dioxide emissions of the countries that have the largest carbon footprint. It shows that if deforestation were a country, it would rank third in yearly carbon dioxide emissions, since cutting down trees releases so much into the atmosphere (World Resources Institute, Global Forest Watch).