What is climate change? Causes and effects of climate change

Climate change is a term used to describe the change in the statistical properties of the climate system over a prolonged period.

Therefore, changes that occur over periods shorter than a few decades, such as El Niño, are not considered to be climate change.

It can be caused by biotic processes, fluctuations in solar radiation, volcanic eruptions, and because of human activities.

Climate change is currently occurring and it is largely caused by human activities, posing significant risks for human and natural systems.

Researchers are constantly trying to learn more about past and future climate through observations and theoretical models. Scientists use general circulation models in theoretical approaches to make future climate projections and link causes and effects.

The causes of climate change

There are internal forcing mechanisms (natural processes within the climate system itself), external forcing mechanisms (from outside our climate system), and human factors. Climate forcing mechanisms “force” the climate to change.

Internal forcing mechanisms

Operates from within the climate system. The earth’s climate system includes the atmosphere, hydrosphere, cryosphere, lithosphere and biosphere. Examples of internal forcing mechanisms include changes in ocean currents and the distribution of species.


The ocean is a key part of the earth’s climate system. However, according to MIT, “the oceans are among the most poorly known and understood, because of the enormous difficulty of probing the deep layers which are still basically void of observations, and the sparseness of data in the southern ocean.”

According to a study published in Journal of Climate, by Dietmar Dommenget, titled “The Ocean’s Role in Continental Climate Variability and Change”:

“A characteristic feature of global warming is the land–sea contrast, with stronger warming over land than over oceans.”

“The ocean’s natural variability and change is leading to variability and change with enhanced magnitudes over the continents, causing much of the longer-time-scale (decadal) global-scale continental climate variability.”

“Model simulations illustrate that continental warming due to anthropogenic forcing (e.g., the warming at the end of the last century or future climate change scenarios) is mostly (80%–90%) indirectly forced by the contemporaneous ocean warming, not directly by local radiative forcing.”


Life can also cause climate change because of its role in carbon and water cycles. Examples of how life has had an impact in the past include: glaciation, which occurred 2.3 billion years ago, and is widely believed to be caused by the evolution of oxygenic photosynthesis.

External forcing mechanisms

External forcing mechanisms operate from outside the Earth’s climate system, and include orbital variations, fluctuations in the solar energy flux, as well as anthropogenic factors (human activities).

Orbital variations

Changes in the Earth’s orbit around the sun can have an impact on seasonal and latitudinal distribution of solar radiation.

There are three types of orbital variations, including changes in Earth’s eccentricity, variations in the tilt angle of Earth’s axis of rotation, and precession of Earth’s axis.

These changes are known as “Milankovitch Cycles” and occur on time scales of 10,000 to 100,000 years. In certain locations the change in energy can be over 10 percent and are known for their correlation to glacial and interglacial periods.

Human factors

There are also anthropogenic factors that can affect the climate. Scientists have concluded that “climate is changing and that these changes are in large part caused by human activities,” and it “is largely irreversible.”

According to the United States National Research Council, “Advancing the Science of Climate Change”:

“Science has made enormous inroads in understanding climate change and its causes, and is beginning to help develop a strong understanding of current and potential impacts that will affect people today and in coming decades. This understanding is crucial because it allows decision makers to place climate change in the context of other large challenges facing the nation and the world. There are still some uncertainties, and there always will be in understanding a complex system like Earth’s climate.”

“Nevertheless, there is a strong, credible body of evidence, based on multiple lines of research, documenting that climate is changing and that these changes are in large part caused by human activities. While much remains to be learned, the core phenomenon, scientific questions, and hypotheses have been examined thoroughly and have stood firm in the face of serious scientific debate and careful evaluation of alternative explanations.”

Greenhouse gases

The warmth of the sun is what makes life on Earth possible. Some of the solar radiation from the sun is bounced back into space, while a small portion is trapped by gases in our atmosphere, acting as a layer of insulation.

Carbon dioxide is the most important gas in this layer of insulation.

Burning fossil fuels (coal, oil and gas) releases carbon dioxide into the atmosphere.

According to The David Suzuki Foundation, our atmosphere now has 42 percent more carbon dioxide than before the industrial era.

The increased amount of carbon dioxide in our atmosphere has turned it into a thick heat-trapping blanket, which causes our climate to change – making it warmer.

Below is an image representing atmospheric carbon dioxide measured at Mauna Loa, Hawaii, from 1960 through 2010. It shows a steady increase in carbon dioxide concentration (ppmv). The image is evidence of the man-made increases in greenhouse gases that are believed to be causing climate change.

atmospheric carbon dioxide

Image created by Robert A. Rohde using NOAA published data.


Consumption beyond our basic needs has been one of the major human factors causing climate change. The goods we demand are becoming increasingly more disposable, thus creating an extremely large amount of waste. In addition, as demand for goods increases the extraction for resources increases. Finally, the disposal of goods also requires energy, the majority of which comes from fossil fuels – increasing CO2 levels in our atmosphere.


When forests are cleared or disturbed, carbon is released as carbon dioxide and other greenhouse gases – contributing to global warming. According to the World Wide Fund for Nature, around one fifth of global greenhouse gas emissions come from deforestation and forest degradation.

Effects of climate change

The effects of climate change include: higher temperatures, changing landscapes, putting wildlife at risk, rising seas, land erosion, stronger storms, more heat-related disease, as well as economic losses.

Higher temperatures

The Earth’s average temperature has increased by one degree Fahrenheit during the 20th century to the highest level in over 400 years. Scientists believe that this is the fastest rise in the average temperature of our planet in a thousand years.

If human factors contributing to climate change isn’t cut back scientists predict that by the end of the century average surface temperatures could rise by 3 to 10 degrees Fahrenheit.

The five hottest years on record have all occurred in the past decade.

Rising sea levels

When the temperature of the planet increases then sea levels rise. This is because warmer water takes up more space than cool water – thermal expansion. As sea temperatures rise glaciers also start melting, which dumps more water into our oceans.

Rising sea levels poses a significant threat to low-lying areas and islands. It can erode shorelines, threaten coastal population, and destroy ecosystems.

Over the past century sea levels have risen between four to eight inches.

Threat to wildlife

The increase in our planet’s temperature changes vegetation patterns, which forces species to move into different areas to survive.

The speed at which climate change is occurring is thought to exceed the migration and adaption abilities of many species. Scientists estimate that a quarter of the Earth’s species will be on the verge of extinction by 2050 if global warming continues.

The Nature Conservancy says that “polar bears could be gone from the planet in as little as 100 years.”

Seawater reacts with the CO2, which is reducing the pH of the oceans. Scientists predict that by the end of the 21st century the pH of the world’s oceans will decline to 7.7, compared to 8 today.

According to a study published in the The Royal Society journal Interface, titled “Ocean acidification alters the material properties of Mytilus edulis shells”, mussel’s shells are becoming more brittle as climate change causes oceans to become increasingly acidic.

With weaker shells, mussels will find it harder to withstand the ocean forces.

Dr Fitzer, lead author of the study, said:

“What we’ve found in the lab is that increased levels of acidification in their habitats have a negative impact on mussels’ ability to create their shells.”

“We worked with colleagues in our School of Engineering to examine the toughness of the shells of the mussels in the more acidic water against those in control conditions. What we found was that the calcite outer shells of the mussels past a certain threshold of acidity was stiffer and harder, making it more brittle and prone to fracture under pressure, and the aragonite inner shell became softer.”

Coral bleaching

With global warming continuing at such an alarming rate ocean temperatures are expected to rise. Scientists predict that climate change will soon cause one of the worst coral bleaching episodes in history. 

Coral reefs provide food and shelter for a wide vast number of small fish and marine species and the health of these reefs is key to sustainable biological diversity.

More intense hurricanes and tropical storms

Some scientists believe that climate change can cause hurricanes and tropical storms to become more intense. This means that storms and hurricanes may last longer, have stronger winds, and cause more damage to costal communities and ecosystems.

The reason behind this is that as the sea temperature rises then developing storms will get more energy from the sea.

Economic loss

Climate change is having an impact on economies around the world. According to a British government report, if action is not taken to cut down global carbon emissions then it could cost between 5 and 20 percent of the annual global gross domestic product.

The same report said that it would only cost 1 percent of GDP to cut the damaging effects of climate change.

In addition, more severe hurricanes and downpours could cause damage to property and infrastructure that would cost billions of dollars.

Evidence of climate change

According to the Intergovernmental Panel on Climate Change:

“In recent decades, changes in climate have caused impacts on natural and human systems on all continents and across the oceans. Impacts are due to observed climate change, irrespective of its cause, indicating the sensitivity of natural and human systems to changing climate.”

“Changes in many extreme weather and climate events have been observed since about 1950. Some of these changes have been linked to human influences, including a decrease in cold temperature extremes, an increase in warm temperature extremes, an increase in extreme high sea levels and an increase in the number of heavy precipitation events in a number of regions.”

Below is a presentation of the “Climate Change 2014: Synthesis Report”. It provides detailed evidence of climate change occurring as well as outlining the threats it poses.