Climate
Change
What is Climate Change?
Climate change, also referred to as global warming, has been clearly stated as a major threat to natural and human systems. The impacts of increasing global temperatures are happening now, and are projected to worsen unless efforts are put together in order to mitigate those risks. In this module, we are exploring the basic concepts of climate science. We outline the difference between climate and weather, so we can understand what is meant when we say that the climate is changing, and how do we know it’s changing. We are breaking down the Earth system into its climate components, both physical and human. Lastly, we are looking at a few solutions that are already in place to mitigate the risks brought by a changing climate.
Learning outcomes
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Definition of climate and climate change
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Consequence of a changing climate
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Solutions in place to mitigate Global Warming
1.1 Climate vs Weather
Some parts of the Earth’s are cold and freezing, like Antarctica, and other parts are warm and sunny, like Puerto Rico or Australia. However, it is also possible to observe snowfall in Australia, or have warm enough days in Antarctica to wear a T-shirt. This brings us to differentiate between weather and climate. Weather is what you get, while climate is what you expect. They are both essential for health, food production, and well-being of humans on a daily basis.
1.1.1 Difference between Weather and Climate
Weather is the short-term changes we observe in the atmospheric conditions such as precipitation, wind, heat, humidity, dryness, sunshine and cloudiness. Weather can vary day-to-day, or even within the same day. Weather events include snowstorm, thunderstorm, heavy rainfall, even hurricanes.
Climate is the prevailing weather conditions in an area, generally averaged over a long period of time. It varies from place to place, depending on the local geography (mountains, sea, latitude), and it varies in time. Temporal variations in climate can be seen locally during the seasonal cycle, or globally over time scales of tens, hundreds or thousands of years. Climate events include droughts, heatwaves, a rainy summers, monsoons, and, on a much longer time scale, ice ages.
1.1.2 The Earth’s climate is changing
Paleo proxies such as tree rings, corals, ice cores and pollens gave us evidences that the Earth’s climate has always been changing. By changes in climate we mean a shift in the average weather conditions. The Earth has been through long periods of warmer temperatures followed by ice ages, each of them lasting over thousands of years.
Changes in climate are attributed to the presence of external forcings, something external to the climate that has an impact on it. Long-term natural climate cycles are caused by natural drivers such as changes in solar radiation and in the Earth’s orbit (also known as the Milankovitch cycle), all occurring on time scales of tens of thousands to hundreds thousands of years. Shorter natural climate cycles (tens to hundreds of years) have also been observed, and are attributed to naturally occurring climatic events like El Nino, volcanic eruptions, or slow and natural changes in carbon dioxide concentrations in the atmosphere.
The figure on the right is showing how the Earth underwent through stages of glaciations and warmer temperature as the precession, obliquity, eccentricity and the solar radiations varied in the past thousands of years.
1.1.3 Recent changes in climate
Recent observations have shown signs of a fast increase in the global mean temperature since the mid-1900s. This global warming has been the cause of what we now call climate change, and scientific evidence discarded the possibility that this is part of the natural climate cycle.
The magnitude in change of global temperatures is much larger than naturally occurring past changes, and are mainly attributed to the increasing emissions of greenhouse gases into the atmosphere, which are unambiguously attributed to human activity. The main difference between past climate changes and the present climate change is that humans are causing it. Human influence on climate is called anthropogenic forcing. Humans, since the Industrial Revolution around 1750, play a crucial role in the present climate changes, and must be accounted for when making predictions for future climate.
Recent changes in the climate system, along with increasing temperatures, include shifts in the global rainfall patterns and hurricanes, increase in heat waves, droughts and flooding events, melting ice sheets and sea ice, and sea-level rise.
1.1.4 Why does Climate Change matter?
An increase in global mean temperature of, 1°C (1.8°F) since pre-industrial reference period (1850-1900) might seem harmless, but it’s imperative to understand that temperature does not increase at the same rate everywhere, and that due to the complexity of the climate system, even a slight change in the average conditions can lead to devastating consequences.
Most importantly, the severity of the impacts caused by global warming are extremely harmful to every aspect of our lives, as well as the natural world. Here are a few examples of major climate change-related threats:
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Increase in droughts affect agriculture (livestock and crops) by water shortage or drier soils, thus possibly increasing food prices, or in certain countries leading to political instability, migration and famine.
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Increase in heavy rainfall due to the air capacity to hold more water vapor as climate warms can lead to an increase risk of flooding, landslide and degrade water quality, all of which are threatening human health and security.
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Biodiversity loss due to unpredictable and extreme climate conditions directly impacts human food security and can possibly lead to an increase in diseases and pests.
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Sea-level rise can flood entire coastal communities, destroying infrastructure and crops permanently, thus dislodging millions of people away from their homes and stripping their traditional livelihood.
1.2 Climate System
The climate system is a highly complex and interactive system. All components, physical and human, interact with each other like a well organized dance. We define here five major physical components: the atmosphere, the hydrosphere, the land surface, the cryosphere and the biosphere; and the human component, the anthroposphere. If we wish to understand the tremendous impact that humans have on our climate, and eventually predict the human influence on the future climate, we need to understand the climate system as a whole and the interactions between its components.
1.2.1 Atmosphere
The atmosphere is the outer layer of gases that surrounds the Earth. It is highly unstable and constantly changing, with air masses rapidly moving vertically and horizontally. It is composed of:
Among those trace gases, only the so-called greenhouse gases interact with infrared radiations emitted by the Earth: carbon dioxide (CO2), methane (CH4), ozone (O3) and nitrous oxide (N2O). Water vapor (H2O) is also an important component of the atmosphere and acts as a powerful greenhouse gas. Other liquid or solid particles called aerosols (e.g. soot, sea salt, dust, volcanic particles) float in the atmosphere and interact with the incoming and outgoing radiations and thus play an important role in climate change.
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78.1% Nitrogen (N2)
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20.9% Oxygen (O2)
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0.93% Argon (Ar)
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0.04% Carbon Dioxide (CO2)
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<0.1% Trace gases
Weather phenomena like cloud formation and precipitation occur in the troposphere, the bottom layer of the atmosphere (up to ~15km). This is also where we find the greenhouse gases. In this layer. Higher in the stratosphere (15-50 km), ozone absorbs ultraviolet solar radiations, a damaging form of radiation. The atmosphere interacts with the ocean and the land through exchanging gases such as CO2, O2 and water vapor.
1.2.2 Hydrosphere
The hydrosphere is composed of every part on Earth that contains liquid water, fresh or saline: clouds, precipitation, subterranean water, rivers and lakes, oceans and seas.
Water moves through the components of the Earth system in what is called the Water Cycle. It is transferred to the atmosphere through evaporation (ocean, rivers and lakes), and through transpiration (plants). Clouds are formed in the troposphere and water returns on land as snow or rain, and back to the ocean through river runoff.
The ocean covers about 70% of the Earth’s surface, and serves as a large reservoir for heat and carbon dioxide, regulating the Earth’s climate by damping strong temperature changes.
The ocean and the atmosphere continuously interact with each other transferring energy, water vapor, oxygen, and carbon dioxide. In fact, the ocean is responsible for about 80% of the oxygen in the atmosphere, produced by marine plants called phytoplankton.
The ocean circulation has a considerable impact on climate and drives some of the climate cycles on longer time scales.
1.2.3 Cryosphere
The cryosphere is the frozen part of the Earth’s hydrosphere. It includes Greenland and Antarctica ice sheets, floating sea ice, continental glaciers, snow fields and permafrost. Its influence on climate is crucial due to its high reflectivity (albedo) for solar radiation, and its critical role in driving the ocean circulation. The large volume of water stored in the ice sheets is a potential source of sea level rise.
Permafrost is a thick layer of frozen ice from years to sometimes hundreds of thousands of years. Collecting ice cores and studying their composition can reveal history of past climates.
1.2.4 Biosphere
The biosphere consists of the sum of all living organisms, marine or terrestrial, ranging from mammals, birds, trees, plants, insects, fish, to microbial life. The biosphere plays an important role on the climate. Terrestrial biosphere transfers water vapor to the atmosphere through evapotranspiration. Vegetation, being darker or lighter than the soil beneath it, can enhance or hinder absorption of solar radiation. Plants, on land or in the ocean, store a significant amount of CO2, and greatly influence the uptake and release of CO2 via photosynthesis, a process where solar energy is captured to transform CO2 into sugar whilst releasing oxygen, making the biosphere an important player in the carbon cycle. Photosynthesis and respiration rates, its inverse process, are greatly impacted by climate change.
The biosphere is also a great source of information for past climates. A lot can be inferred by looking at paleo proxies such as fossils, tree rings, pollen and corals. Those preserved materials help us with our understanding of the present climate.
1.2.5 Land surface
The surface layer of the Earth is composed of soil and vegetation, which interact with the atmosphere via several mechanisms. It partially controls the atmospheric temperature due to its interaction with solar energy, through its albedo. The darker the surface the more radiation it can absorb.
The texture of the land surface, determined by the topography and the vegetation type, impacts the global wind patterns and the transport of atmospheric aerosols like dust which interacts with the atmospheric radiations.
1.2.6 Anthroposphere
Humans are technically part of the biosphere, but are considered separately in the context of the climate system since its impact on the planet is considerable. This human forcing on climate is called anthropogenic forcing. The two major contributions of anthropogenic forcing to climate variability are emissions of greenhouse gases and land-use change. Burning fossil fuels emit gases such as CO2 and CH4 which trap Earth radiations and increase the global temperature. Land-use change, such as deforestation, and cropland harvest, reduce the atmospheric CO2 intake by plants, which also contributes to increasing global temperature. Other harmful impacts include:
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Extensive use of nitrogen fertilizers in agriculture, which provoke harmful algal blooms
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Peat fires which release greenhouse gases
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Irrigation
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Drainage of waste waters
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Atmospheric pollution
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Urban development
Practices such as afforestation, and shifting towards renewable energy can in turn reduce the emissions of greenhouse gases and mitigate global warming. Humans have also largely impacted coastlines, enhancing coastal erosions, and replaced land surface vegetation covers with roads and cities, thus creating heat islands and reducing migration corridors for many animals.
1.3 Climate Actions
Climate change is becoming a major threat for all of Earth’s inhabitants: humans and wild life. Global increase in temperature, sea level rise, ice sheets melting, increased wild fires, droughts and floods are all threats to human health, food security, and national security. Human population keeps increasing, thereby increasing demand for food and energy supplies, making it crucial to mitigate climate change impacts by reducing emissions, shift towards more sustainable practices and reduce waste. The Earth has warmed about 1°C (1.8°F) since the beginning of the Industrial Revolution. Thankfully, we have the ability to change our fate, and efforts are already on their way to limit the temperature increase to 1.5°C (3°F), and eventually reach a net-zero emission.
1.3.1 Why should we keep the temperature increase under 1.5°C?
The Intergovernmental Panel for Climate Change (IPCC) is pressing for keeping the ongoing temperature increase under 1.5°C (3°F). According to their assessment report, limiting the global temperature increase to 1.5°C is less damageable than a 2°C warming, and requires less effort and adaptation.
Under an increase of 2°C (4°F), the Arctic could be completely free of sea ice in summer, whilst only a few times a century under 1.5°C. Coral reefs would be eradicated at 99% instead of 70-90%. Severe heat waves would hit hundreds of million more people, exposing 200-300 million more people to water shortages.
It is clear that any warming has devastating consequences on humans: risks for livelihoods, food and water security, human health and security, economic growth. Nevertheless, global CO2 emissions will have to be reduces to zero in the next 30 years, which will require international and sustained efforts in all economic sectors.
Intergovernmental Panel for Climate Change (IPCC) is a group of scientists from over 130 countries that was created to assess the science of climate change, its potential risks and future implications.
1.3.2 Pathways to limit CO2 emissions
The only way to stabilize global temperature is to stop emitting CO2 to the atmosphere. The goal is to achieve a net-zero emission, which can be done via either completely stop all emissions, or significantly reduce emissions and balancing the remaining emission using carbon sequestration technologies to remove CO2 from the atmosphere.
An example of such technologies is bioenergy with carbon capture (BECCS), which involves burning biomass coupled with direct capture of atmospheric CO2 and storage in geological reservoirs. This technique would yield net-negative emissions. Implementing such technologies on a large-scale is certainly a challenge, and also raise concerns as to whether growing crops would be used for fuel instead of food.
What we need to do
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Reduce global energy, materials and food demand
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Use energy and materials more efficiently
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Improve agricultural practices to reduce emissions and water use
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Transform the make-up of global energy supply.
Renewable energies (biomass, wind, hydropower and solar) are on the rise and technologies are becoming more efficient, which could make it possible to supply two-thirds of primary energy by 2050 and, along with behavioral changes, help achieve the 1.5°C limit.
1.3.3 What strategies can we adopt? What are the ethical questions we need to pose?
To mitigate climate change impacts, we need to find long-term goals that are relevant to limit the temperature increase, meanwhile evaluating risks and taking into consideration the greater vulnerability of certain communities. International cooperation is fundamental, and initiatives are already on their way to achieve the 1.5°C goal. A few of them are listed in the table below.
1.3.4 Net-zero emissions: Ongoing initiatives
Paris Agreement
Legally binding international treaty on climate change adopted by 196 Parties at COP 21 in Paris in 2015.
UN Sustainable
Development Goals
17 goals adopted by all UN members in 2015 for a more sustainable future, tackling poverty, inequality, climate change, environmental degradation, peace and justice.
US National Climate Assessment
The NCA assesses the science of climate change and variability and its impacts across the US.
Climate Assembly UK
A commitment from the UK to reach net zero emissions by 2050, underpinning education, choice, fairness and political consensus.
