The Science Behind Climate Change
1.0 Module Learning Objectives
After completion of this module, you will be able to:
Discuss the science behind climate change
Explain how we know human-caused climate change is real
Explain what a carbon sink is and describe what the carbon cycle is
Explain what governments around the world are doing to combat climate change
1.1 What is Climate Change?
Climate is the average weather in a place over the course of many years. Climate change is a shift in those average weather conditions. Earth’s climate has changed naturally throughout history. Natural causes of climate change include variations in the Sun’s solar output, changes in Earth’s rotation and orbit, ocean currents, large volcanic eruptions, and slow changes in the concentrations of greenhouse gases in the Earth’s atmosphere.
Scientists can track these natural changes in climate by examining ice cores drilled from Greenland and Antarctica, tree rings, glaciers, pollen remains, and ocean sediments to provide evidence of climate conditions as far back as 800,000 years ago. Research has been able to prove that these naturally-occurring phenomena cause the planet to cycle between periods of warmth and ice ages.
Image 1.1 As snow falls and begins to settle on an ice sheet, it traps small pockets of air. Over time, the snow compresses until the trapped air is pressed into the structure of the ice itself. The snow layers also collect soot and dust that settle on the snow. By drilling deep down into ice sheets, scientists can analyze the air, soot and dust in the ice cores to determine a year-by-year record of climates from the past.
1.2 What is the Greenhouse Effect?
Most of the solar energy that is emitted from the sun passes through earth’s atmosphere and to the earth’s surface and is absorbed by the land and oceans and heats the planet. Some of that solar energy that reaches earth’s surface is reflected back to earth’s atmosphere and then into space. While some of this energy continues on into space, most of the energy gets absorbed by atmospheric gases, known as greenhouse gases, and redirected back toward the earth, causing further warming.
Greenhouse gases like carbon dioxide (CO2), methane, nitrous oxide, and water vapor are vital to keeping earth inhabitable. Together, greenhouse gases act like a blanket that covers the earth, keeping the earth warmer than it would otherwise be. This “blanket” is called the greenhouse gas effect.
Image 1.2 Greenhouse gases in the atmosphere absorb heat, slowing or preventing the loss of heat into space. More greenhouse gases in the atmosphere have caused an enhanced greenhouse effect, which has caused earth's energy balance to be thrown off.
Human activities have led to an enhanced greenhouse effect.
Carbon dioxide and other greenhouse gases are released into the atmosphere through activities like deforestation, agriculture, putting organic material in our landfills, and burning fossil fuels like coal and natural gas to power our homes, businesses, and cars. Because of these activities, an increase in greenhouse gases in earth’s atmosphere has created a much thicker “blanket” around earth, making it harder for heat to release back into space. This has resulted in higher global temperatures that have led to drastic changes in the Earth’s climate.
Concentrations of greenhouse gases in our atmosphere have increased at unprecedented levels.
Image 1.3 For most of the past 800,000 years, the concentrations of greenhouse gases in our atmosphere has been between 200 and 280 parts per million. This means that there were 200 to 280 molecules of greenhouse gases per million molecules of air. In the past hundred years, that concentration has increased to around 420 parts per million. That big of a jump in concentration is unprecedented in earth's 4.5 billion year history, and can only have been caused by human activity.
Image 1.4 High carbon dioxide levels (in blue) over the past 800,000 years of Earth’s history have corresponded to high temperatures (in red) and low carbon dioxide levels have corresponded to low temperatures.
Greenhouse gases are linked to higher temperatures.
The recent buildup of greenhouse gases in the atmosphere from human activities has changed the earth's climate and resulted in dangerous effects to human health and welfare and to ecosystems around the globe. Furthermore, it has been proven that rising levels of greenhouse gases like carbon dioxide are linked to higher temperatures.
1.3 What is the evidence of human-caused climate change?
The video on the left shows a time lapse of the average temperature changes on Earth's surface from the year 1880 to the year 2021. As the years pass, you can see the amount of yellow and orange spots increasing, which correspond to an increase of 1 to 2 degrees Celsius over much of the planet. Human activities that release greenhouse gases into the atmosphere have caused Earth to warm by about 1.7 degrees Fahrenheit since 1880.
What are the measurable facts?
According to the National Oceanic and Atmospheric Administration's (NOAA) temperature data, 2020 was the second warmest year on record
The 10 warmest years on record have occurred since 2005
The top 100 meters of the world's oceans have been an average of 0.6 degrees Fahrenheit warmer since 1969
According to NASA, Greenland lost an average of 279 billion tons of ice per year between 1993 and 2019, while Antarctica lost about 148 billion tons of ice per year
Global sea level rose about 8 inches in the last hundred years
Glaciers are retreating almost everywhere around the world
Image 1.5 Decreased glacier and snow cover, decreased sea ice, a rise in sea level, an increase in humidity, and an increase in land and ocean temperatures are all indicators of a warming climate.
Image 1.6 As mentioned earlier, many natural factors affect the climate, including changes in the Sun’s output or the Earth’s orbit and large volcanic eruptions. Scientists measure these effects, but none can account for the observed trends. Scientists can only account for recent global warming by including the effects of human greenhouse gas emissions. The green part of the graph shows that accounting for only these natural factors cannot explain the level of warming that has been observed over the past century. The blue part of the graph shows that accounting for both natural factors and human-caused emissions can explain the level of warming that has been observed over the past century.
Photo Source
Image 1.7 Earth’s temperature has risen by 0.14° F per decade since 1880, and the rate of warming over the past 40 years is more than twice that: 0.32° F per decade since 1981. If these trends continue, disasters will destabilize entire countries, send millions of people into refugee camps, cause mass extinctions, and raise sea levels to the point where thousands of coastal cities will be under water.
Photo Source1.4 The importance of the carbon cycle and carbon sinks
The Carbon Cycle
Image 1.8 Carbon is the backbone to all life on Earth. It is in the air we breathe, the food we eat, and it’s even in us. There are approximately 121 million gigatons of carbon on or near earth's surface, and that carbon constantly flows between the atmosphere, the ocean, sediments, and organisms on earth. This process is known as the carbon cycle. Normally, the carbon cycle keeps Earth’s carbon levels in balance. However, the carbon cycle is being thrown out of balance because of human activities.
What is a Carbon Sink?
Plants, sediments, and the oceans are all carbon sinks, which means that they absorb and store more carbon than they release into the atmosphere. Carbon sinks are extremely important to the carbon cycle because they store excess carbon and keep the greenhouse gas “blanket” from getting even thicker. Of the 121 million gigatons of carbon on or near earth's surface, 78 million gigatons is stored in limestone, sediments and fossil fuels; 41 million gigatons is stored in the world's oceans; 3,300 gigatons is held on the land; and 885 gigatons is in the atmosphere in gaseous form as carbon dioxide. However, increased human activity is now releasing more carbon into the atmosphere (in the form of carbon dioxide) than the Earth’s natural carbon sinks can absorb. When plants and trees die from deforestation, they release the carbon they were storing into the atmosphere. The process of drilling and mining fossil fuels is energy-intensive and also emits carbon dioxide into the atmosphere. As a result, the amount of carbon in the atmosphere is rising.
Image 1.9 The world's forests absorb and store billions of tons of carbon from the atmosphere through photosynthesis. When forests are cut down, the carbon they store is rereleased into the atmosphere.
Image 1.10 Permafrost is permanently frozen ground that covers much of the Arctic tundra in Alaska, Siberia, Canada and Greenland. Arctic permafrost is estimated to store twice as much carbon than is in the atmosphere. If warming trends continue, permafrost will thaw and release these carbon stores into the atmosphere.
Image 1.11 The world's oceans absorb around one third of global carbon emissions. The increased carbon emissions from human activities continues to increase ocean surface water temperature, slow the ocean's ability to absorb carbon, acidify the water, and harm marine life.
1.5 What is the world doing about the climate crisis?
The IPCC
The Intergovernmental Panel on Climate Change (IPCC) was created by the United Nations and the World Meteorological Organization to provide governments and stakeholders around the world with evidence of Earth’s climate crisis. The IPCC, which is supported by 195 countries, enlists experts from around the world to draft scientific assessments on climate change, its impacts, and mitigation and adaptation strategies. The IPCC has found that the “scientific evidence for warming of the climate system is unequivocal”, and that human activities are the cause.
IPCC Tipping Points
Image 1.12 Twenty years ago the IPCC introduced the concept of tipping points, the points at which small changes in the carbon cycle become large enough to cause an irreversible change that will have cascading effects. According to the most recent IPCC report, if global temperatures increase between 1 degree and 2 degrees Celsius, major tipping points in the climate system will be reached. Some of the major tipping points include the melting of the Greenland ice sheet, which would raise global sea levels by over 20 feet; widespread thawing of permafrost, which stores two times more carbon than Earth’s atmosphere; and continued dieback of the Amazon rainforest, which is responsible for helping to stabilize the global climate.
The Paris Agreement
The Paris Agreement is a legally binding international climate change treaty that was adopted by 191 countries and entered into force in 2016. The goal of the Paris Agreement is to prevent major tipping points from being reached by limiting global warming to 1.5 degrees Celsius above pre-industrial levels. To do this, all countries must cut their greenhouse gas emissions in half by 2030 and be net-zero by 2050. Net-zero means achieving a balance between anthropogenic emissions by sources and removals by carbon sinks. Achieving net-zero will involve transitioning from fossil fuels to renewable energy for our power, replacing vehicles that run on gas with electric vehicles, and changing land use practices.
Is the Paris Agreement enough?
The Paris Agreement is the first collective effort by all countries to address climate change. Every five years, each country is expected to submit an updated national climate action plan - known as Nationally Determined Contribution, or NDC. In their NDCs, countries communicate actions they will take to reduce their greenhouse gas emissions in order to reach the goals of the Paris Agreement. However, of the 191 countries that signed the agreement, only two countries - Morocco and Gambia - have set targets that are consistent with the 1.5 degrees Celsius limit. None of the world's seven most advanced economies - the United States, Canada, Japan, Germany, Italy, France and the United Kingdom - have come close to setting targets that are in alignment with the Paris Agreement.
1.6 What is CLPCCD doing?
In 2019, Chabot and Las Positas updated their Climate Action Plans. A greenhouse gas inventory was conducted for both colleges, which determined how much emissions each college is responsible for. Greenhouse gas inventories are important because they give institutions the ability to set goals for emissions reductions and climate mitigation strategies.
1.7 Calls to Action
What can you do?
Find your carbon footprint using this link. Finding your carbon footprint will give you a sense of how much greenhouse gases your daily activities emit.
Support CLPCCD's sustainability initiatives, or start one at your office.
Express your concerns about climate change in an email to Senator Feinstein and Senator Padilla.
Attend a Council Sustainability Committee meeting to learn about climate initiatives by the City of Hayward.
Go to the Climate Action Mapping Project to find organizations that are focused on climate action in the Bay Area.
Use the resources below to educate yourself on the climate crisis.
Books
Drawdown by Paul Hawken
How to Avoid a Climate Disaster: The Solutions We Have and the Breakthroughs We Need by Bill Gates
The Uninhabitable Earth by David Wallace-Wells
No One Is Too Small to Make a Difference by Greta Thunberg