The Earth’s climate has been changing throughout the history. Just in the last 650,000 years there have been seven cycles of glacial advance and retreat, with the end of the last ice age about 7,000 years ago, at the beginning of human civilization. Most of these climate changes were gradual and attributed to very small variations in Earth’s orbit that change the amount of solar energy our planet receives .
Sadly, that is not what is happening today. The warming trend we are experiencing has been proceeding at an “unprecedented rate” since the mid-20th century according to NASA, and is “extremely likely” (higher than 95 percent probability) the result of human activity .
The concept that humans can change the climate of our environment is not a modern one as there are accounts of ancient Greeks and 19th century Americans debating how cutting down forests might bring more rainfall to a region, or less.
Already in the 1930’s, people realized that the region of the United States and the North Atlantic had warmed significantly during the previous half‑century. At the time, it was unclear why this has happened and the potential for this change to have occurred due to human activity was not considered a real possibility.
It was really only G. S. Callendar who insisted that greenhouse warming was the cause. The view did not gain any real traction until the 1950’s, when scientists were able to employ improved techniques and calculations to confirm that carbon dioxide could build up in the atmosphere raising temperatures.
By 1960, the painstaking measurements of C. D. Keeling provided irrefutable proof that the levels of greenhouse gases were increasing, year by year.
Today, we know that the global average temperature has risen by about 1 degrees Celsius since the late 1900’s which among other impacts has led to declining glaciers and sea ice while the global sea level has risen by about 8 inches (21 centimetres). At the same time, increased carbon dioxide levels are causing the oceans to become more acidic impacting aquatic ecosystems.
This is particularly concerning if one considers that with no action to tackle climate change, global temperatures could increase by 7 degrees Celsius or more . But how does climate change actually happen?
What causes climate change?
The scientific consensus is that human activity is causing climate change.
More specifically, in its Sixth Assessment Report, the Intergovernmental Panel on Climate Change (IPCC), made up of 1,300 independent scientific experts from countries across the world and operating under the auspices of the United Nations, concluded that the pro probability that human activities have warmed our planet over the past 50 years is over 95 percent .
This is as clear as science can be.
While in the past our climate did undergo radical changes, it did so over many thousands of years; this is not the same kind of change as we are seeing today.
For example, at times, the UK was hot enough for hippos lived in Norfolk while at other times ice has covered the country for tens of thousands of years . Global climate change has usually occurred very slowly. Today our climate is changing very quickly.
Current climate change is a result of an excessive amount of carbon dioxide and other greenhouse gases in the earth’s atmosphere. The amount of carbon dioxide in the atmosphere has risen by 34 percent since the 17th century.
How exactly does carbon dioxide and other greenhouse gases affect global climate?
Life on our planet depends on energy coming from the Sun. When the light from the Sun reaches the Earth’s atmosphere, it passes through the air and clouds to the surface, where it is absorbed and radiated upward in the form of infrared heat.
90 percent of this heat is then absorbed by greenhouse gases (e.g. carbon dioxide, methane and nitrous oxide or water vapor) and radiated back towards the surface, which is then warmed to about 15 degrees Celsius (59 degrees Fahrenheit) which is a temperature that enables life on Earth.
Carbon dioxide is one of the greenhouse gases. It is nearly transparent to solar radiation emitted from the sun, but partially opaque to the thermal radiation emitted by the earth which means that it is pretty efficient in trapping the heat in the atmosphere. That is why it has been described as a greenhouse and that is why warming due to excess carbon dioxide trapping heat in our atmosphere is commonly called “the greenhouse effect.”
Many natural activities can alter the concentration of greenhouse gases in the atmosphere, for example volcanic activity. But over the last two centuries, changes in the atmosphere have come about as a result of the Industrial Revolution.
This is because industrial production has resulted in increased emissions of greenhouse gases. And since these gases, when released into the atmosphere, block heat from escaping, they have been increasing the earth’s temperature.
Once the carbon is emitted into the atmosphere, it sticks around for hundreds of years, some of it even longer, trapping heat. The effects of this are cumulative, growing more severe with time.
Carbon dioxide is the greenhouse gas that is most commonly produced by human activities and it is responsible for 64 percent of man-made global warming. Its concentration in the atmosphere is currently 40 percent higher compared to pre-industrialization levels.
Today, so much carbon has been allowed to accumulate in the atmosphere that to keep warming below the internationally agreed-upon target of 2 degrees Celsius wealthy countries will have to cut their emissions by at the very least 8 to 10 percent a year .
Some other greenhouse gases are emitted in smaller quantities, but they actually trap heat far more effectively than carbon dioxide: for example, methane is responsible for 17 percent of man-made global warming and nitrous oxide for 6 percent .
Other greenhouse gases include water vapor, which despite being the most abundant of these gases does not produce the same effect as its level in the atmosphere depends on temperatures, and nitrous oxide with fluorinated gases.
One indication that the global climate is changing are the rising sea levels. Globally, the sea levels rose about 8 inches (21 centimetres) in the 20th century. And in the last two decades, the sea has risen at a rate nearly double of the last century. This is because the oceans are absorbing more than 90 percent of the increased heat caused by carbon dioxide emissions from human activity. This increased heat causes the water to expand. Secondly, it is rising due to ice melting from glaciers and ice sheets .
But what human activities are causing such a dramatic increase in greenhouse gas emissions in the first place?
What are the biggest contributors to climate change?
There is a variety of activities that contribute to the release of greenhouse gases.
#1 Fossil fuels
Oil, coal and natural gas used to produce electricity and heat are responsible for more than 25 percent of global greenhouse gas emissions . Carbon dioxide and nitrous oxide are released by burning coal, oil and gas. Even though oil is considered one of the dirtiest fossil fuels, it still is the main global energy source and it is responsible for producing 46 percent of global carbon dioxide emissions, according to data gathered in 2003 .
Generous subsidies continue to support fossil fuel investment, despite growing evidence that clean energy can be lower-risk and often lower-cost.
Clean energy is an essential alternative considering that more than 1.2 billion people in the world do not yet have electricity and it is very likely that soon they will also need to have access to this modern age necessity.
Emissions from transport sector account for almost 25 percent of carbon dioxide release . Sustainable low carbon mobility options must be developed to reduce them.
Developed countries are making efforts to increase low-carbon public transportation and developing countries are implementing initiatives to reduce emissions both in freight transport and personal transportation through urban mobility planning.
However, despite these efforts, emissions are still very high. More actions to tackle this issue need to be taken and more quickly.
#3 Manufacturing and construction
Manufacturing and construction accounted for over 19 percent of emissions in 2014 . The outcry from industry and their Congressmen fighting clean air legislation which would impose curbs on their emissions, declaring that they will have to shut down factories and jobs will be lost, is used to rally support from unaware people through the use of fear.
For over 80 percent of U.S. manufacturers, the annual cost of all current environmental controls is less than 1 percent of their value of product shipments.
#4 Agriculture and forestry
While our industrial activities, energy generation and transport are major emitters of greenhouse gases, there are other ways in which humans have contributed to the increase of greenhouse gases. For example, livestock farming, such as cows and sheep produce large amounts of methane when they digest their food. And fertilizers used in agriculture produce nitrous oxide emissions.
Agriculture and forestry are responsible for over 24 percent of the emissions globally and 9 percent of carbon emissions in the United States . If figures were added in for the components of modern industrial agricultural practices of spraying pesticides and fertilizers that figure jumps up to 30 percent emissions for the United States .
Deforestation for agriculture land use means the forests can no longer absorb the carbon dioxide. On contrary, cutting down forests means that the carbon stored in trees is released into the atmosphere while we can no longer benefit from their ability to act as carbon sinks. And although organic agriculture can remove from the air and sequester 7,000 pounds of carbon dioxide per acre per year , intensively managed agricultural land farmed with pesticides and fertilizers cannot.
Two of the biggest culprits in the agriculture sector making headlines today for inordinate releases of another greenhouse gas, methane, are the cattle industry in the United States and the rice paddies in Asia.
Widespread changes in personal consumer choices could significantly affect the agriculture contribution to global warming.
- Buying locally translates into reduced emissions from transportation.
- Eating organic food will reduce demand for food that is grown using heavily polluting modern industrial practices.
- Reducing meat and rice consumption will reduce the demand for two products that contribute heavily to greenhouse gas emissions.
There is a lot of scientific evidence supporting the case that human activity is contributing to the kind of climate change we are experiencing today. Understanding the basic science behind climate change is key information in today’s world. Informed citizens are critical to tackling this issue with the right policies.