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Climate Crisis

This guide provides information, resources, and data on the climate crisis

What is Climate Change?

What is Climate Change?

In common usage, climate change describes global warming -- the ongoing increase in global average temperature -- and its effects on Earth's climate system. The current rise in global average temperature is far more rapid than previous changes, and due to human actions.

Fossil fuels – coal, oil and gas – are by far the largest contributor to global climate change, accounting for over 75 per cent of global greenhouse gas emissions and nearly 90 per cent of all carbon dioxide emissions. Larger amounts of these gases trap more heat in Earth's lower atmosphere, causing global warming.

What are Greenhouse Gases?

Greenhouse gases are transparent to sunlight, and thus allow it to pass through the atmosphere to heat the Earth's surface. The Earth radiates it as heat, and greenhouse gases absorb a portion of it. This absorption slows the rate at which heat escapes into space, trapping heat near the Earth's surface and warming it over time. This is called the Greenhouse Effect. Without the naturally-occurring greenhouse effect, the air temperature near Earth's surface would be about 33 °C colder than the average pre-industrial revolution temperature, thus this absorption of heat is what allows the planet to be habitable to most life on earth.

Since the Industrial Revolution (the transition to machine manufacturing processes in the late 18th century), humans are the biggest contributor to greenhouse gases, mostly through extracting and burning fossil fuels (coal, oil, natural gas) which increase concentrations of CO2 into the atmosphere. Many other industrial and agricultural processes also increase emissions CO2 emissions. Methane emissions, mainly caused by livestock, also account for the increase in greenhouse gases.

Causes of Climate Change
  • Electricity -- globally, most electricity and heat is still generated through fossil fuels, causing a significant portion of the global greenhouse gas emissions
  • Manufacturing -- manufacturing and industry practices produce emissions through burning fossil fuels, but also many of the chemicals that are produced through these processes also contribute to greenhouse emissions and other toxic by-products
  • Deforestation -- cutting down forests (either for agricultural or commercial reasons) not only decreases the number of trees that naturally help absorb carbon dioxide in the atmosphere and replenish oxygen, but when trees are cut down they end up releasing the carbon dioxide they have absorbed and stored back into the atmosphere
  • Food Production -- producing food causes both carbon dioxide and methane emissions, through deforestation necessary farming and pastures, but also from the digestion processes of livestock, the energy needed to run farming equipment, and the fertilizers used to prevent crops from dying. The processing and distribution of food through manufacturing and transportation also increases emissions.
  • Transportation -- nearly all forms of transportation (cars, trucks, planes, trains, and ships) run on fossil fuels. Shipping and commuter traffic are the biggest causes of emissions due to transportation, primarily road-based but in recent years planes and ships have increased their share.
  • Consumerism -- the way we live also contributes to greenhouse gas emissions, from how we run and heat our homes, to what we eat and the clothes we wear, to our electronics and toys. The wealthiest bear the greatest responsibility: the richest 1 per cent of the global population combined account for more greenhouse gas emissions than the poorest 50 per cent.

Global Temperature Rise

According to IPCC Sixth Assessment Report, in the last 170 years, humans have caused the global temperature to increase to the highest level in the last 2,000 years. The current multi-century period is the warmest in the past 100,000 years. The temperature in the years 2011-2020 was 1.09°C higher than in 1859-1890 (pre-industrial baseline). The temperature on land rose by 1.59°C while over the ocean it rose only by 0.88°C. Since 1950, the number of cold days and nights has decreased, and the number of warm days and nights has increased.

While there have been periods of global warming throughout Earth's history, the modern observed rise in temperature and CO2 concentrations has been so rapid that even abrupt geophysical events (volcanic explosions, meteorite impacts, etc.) in Earth's history do not approach current rates.

Evidence of warming from air temperature measurements are reinforced with a wide range of other observations, such as changes to the natural water cycle (increased frequency and intensity of heavy precipitation, increased melting snow and ice, increased humidity). Other signs, such as plants flowering earlier in spring also are observed evidence of warming air temperatures.

Climate Variability

Regions of the world warm at differing rates. The pattern is independent of where greenhouse gases are emitted, because the gases persist long enough to diffuse across the planet. Since the pre-industrial period, the average surface temperature over land regions has increased almost twice as fast as the global-average surface temperature.

The Northern Hemisphere and the North Pole have generally warmed much faster than the South Pole and Southern Hemisphere. The Northern Hemisphere not only has much more land, but also more seasonal snow cover and sea ice. As these surfaces flip from reflecting a lot of light to being dark after the ice has melted, they start absorbing more heat. Local black carbon deposits on snow and ice also contribute to Arctic warming. Arctic temperatures are increasing at over twice the rate of the rest of the world. Melting of glaciers and ice sheets in the Arctic disrupts ocean circulation, including a weakened Gulf Stream, further changing the climate.


Many people think climate change mainly means warmer temperatures. But temperature rise is only the beginning of the story. Because the Earth is a system, where everything is connected, changes in one area can influence changes in all others.

The consequences of climate change now include, among others, intense droughts, water scarcity, severe fires, rising sea levels, flooding, melting polar ice, catastrophic storms and declining biodiversity.

Climate change can affect our health, ability to grow food, housing, safety and work. Some of us are already more vulnerable to climate impacts, such as people living in small island nations and other developing countries. Conditions like sea-level rise and saltwater intrusion have advanced to the point where whole communities have had to relocate, and protracted droughts are putting people at risk of famine. In the future, the number of “climate refugees” is expected to rise.

What is the Climate Crisis?

The climate crisis (also referred to as a climate emergency) is the decisive tipping point of climate change, seen as the "point of no return" where the future of life on earth is in peril.

World Scientists' Warning to Humanity

In 1992, Henry Kendall, the former chair of the Union of Concerned Scientists (UCS) wrote the first warning on climate change and a future climate crisis. His 1992 document began with: "Human beings and the natural world are on a collision course." It was co-signed by 1,700 of the world's leading scientists and a majority of the world's Nobel Laureates in science. This petition recommended that the world at large must:

  • move away from fossil fuels to more benign, inexhaustible energy sources
  • cut greenhouse gas emissions
  • clean the pollution of our air and water
  • stabilize the population

Twenty five year later, in November 2017 a "Second Notice" to the Warning to Humanity was written by William Ripple, a world-renowned ecologist at Oregon State University. This declaration was signed by 15,364 scientists. This warning called for the global changes to address, among other things:

  • limit population growth
  • drastically diminish fossil fuel consumption
  • drastically diminish meat consumption

The second notice also included 9 time-series graphs of key indicators, each correlated to a specific issue mentioned in the original 1992 warning, to show that most environmental issues are continuing to trend in the wrong direction, most with no discernible change in rate. The article included 13 specific steps humanity could take to transition to sustainability. The second notice has more scientist cosigners and formal supporters than any other journal article ever published.

Climate Emergency Declaration

In November 2019, a group of over 11,000 scientists from 153 different countries proclaimed that the earth was in a climate emergency that would lead to "untold human suffering" if no big shifts in action take place.

We declare clearly and unequivocally that planet Earth is facing a climate emergency. To secure a sustainable future, we must change how we live. [This] entails major transformations in the ways our global society functions and interacts with natural ecosystems.

The emergency declaration highlighted that economic and population growth are the primary drivers of CO2 emissions from fossil fuel consumption, and that "we need bold and drastic transformations regarding economic and population policies".

The declaration was updated in 2021 with 31 vital signs that need to be addressed and changed, including:

  • greenhouse gases
  • global surface temperatures
  • rising sea levels
  • energy use
  • ice mass
  • global ocean temperatures
  • loss of rainforest

Of these 31 signs, 18 of them are already seen as reaching critical levels, and that the only profound change in human behavior will change the trajectory.

They point to six areas where fundamental changes need to be made:
  1. energy -- eliminating fossil fuels and shifting to renewables
  2. short-lived air pollutants -- slashing black carbon (soot), methane, and hydrofluorocarbons
  3. nature -- restoring and permanently protecting Earth's ecosystems to store and accumulate carbon and restore biodiversity
  4. food -- switching to mostly plant-based diets, reducing food waste, and improving cropping practices
  5. economy -- moving from indefinite GDP growth and overconsumption by the wealthy to ecological economics and a circular economy, in which prices reflect the full environmental costs of goods and services
  6. human population -- stabilizing and gradually reducing the population by providing voluntary family planning and supporting education and rights for all girls and young women, which has been proven to lower fertility rates


In October 2022, at the 30th anniversary of the initial publication of the "World Scientists' Warning to Humanity", a second update to the climate emergency declaration concluded that "We are now at 'code red' on planet Earth."