Climate Literacy Quiz

Answer - Certain gases in the atmosphere trap heat and warm the Earth

×

Provenance: NASA http://climate.nasa.gov/causes/
Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

The greenhouse effect is a natural phenomenon. Certain gases in the atmosphere have the ability to absorb radiation that would otherwise escape into space. The greenhouse effect is somewhat like a blanket that retains your body heat and keeps you warm.

Gases that trap heat are called greenhouse gases and they include water vapor, carbon dioxide, methane, and nitrogen oxides. These gases can have potent effects even in small quantities.

Without this natural greenhouse effect, the Earth's average temperature would be below freezing!

Note that answer c, 'The tilt of the Earth changes the amount of solar energy the Earth receives,' is also true, but is not related to the greenhouse effect. Variations in the tilt and orbit of Earth do affect how much solar radiation reaches the Earth, and this is one of many natural variations in our climate system.

Note also that answer b, 'Life exhales gas that warms up the atmosphere,' is partly true. Some life forms, like humans and mammals exhale CO₂, but this CO₂ only recently came out of the atmosphere. Plants use up CO₂ to make carbohydrates/sugar/which?, animals eat the plants and return the CO₂ to the atmosphere. This is an example of a short-term process within the carbon cycle, and it balances out from year to year. By contrast burning fossil fuels rapidly releases carbon that has been stored in Earth's crust for millions of years.

Learn more from Does breathing contribute to CO₂ buildup in the atmosphere? from Skeptical Science.

×

Hurricane Sandy is seen churning towards the east coast of the United States is this NOAA handout satellite image taken on October 27, 2012.

Provenance: National Oceanic and Atmospheric Administration
Reuse: This item is in the public domain and maybe reused freely without restriction.

While the greenhouse effect is natural and in fact, helps maintain a climate suitable for life as we know it, humans have altered a natural process. A small change in the amount of greenhouse gases in the atmosphere has a large and long-lasting effect. Furthermore, humans have changed the composition of the atmosphere over a short time span, and the resulting warming us many times faster than natural changes. We are already seeing consequences like heat waves, melting sea ice, rising sea level, increased wildfires, and increases in extreme weather.

×

Show caption

Hide

Sources of greenhouse gas emissions from various sectors in the USA. Different types of greenhouse gases are converted to "CO2 equivalent" so that all types of greenhouse emissions can be compared on one graph. Data from 2019. Image from the EPA. Source: [https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions]. This data is updated yearly and the link goes to the current data.

Provenance: From the US EPA
Reuse: This item is in the public domain and maybe reused freely without restriction.

In the USA, greenhouse gas emissions from electricity are falling as coal burning is slowly declining. Thus, the proportion of emissions from transportation has grown, and it accounted for 29% of total USA emissions in 2019, according to EPA data.

×

Global sources of greenhouse gas emissions from various sectors. Different types of greenhouse gases are converted to "CO2 equivalent" so that all types of greenhouse emissions can be compared on one graph. Data from 2015. Image by Karin Kirk for CLEAN. Data from www.climatewatchdata.org.

Provenance: Karin Kirk, Freelance Science Writer and Geoscientist
Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

Sources

Sources of Greenhouse Gas Emissions, USA - from the EPA, updated yearly

Global Emissions trends and sources, from The Center for Climate and Energy Solutions

Global Historical Emissions - interactive graph by Climate Watch

×

Show caption

Hide

Carbon dioxide in the atmosphere over the past 400,000 years. The difference between the natural rhythm of the ice ages and the exponential rise of CO2 over the past 100 years is starkly apparent. Humans have altered the composition of Earth's atmosphere, and therefore we have also changed Earth's energy balance. Image from NASA. Source: [https://climate.nasa.gov/evidence/]

Provenance: From NASA
Reuse: This item is in the public domain and maybe reused freely without restriction.

From 1751-2018, humans added 1,611 billion tons of carbon to the atmosphere in the form of carbon dioxide. Around 80% of all human-produced carbon dioxide comes from burning coal, natural gas, oil and gasoline.

When today's CO₂ trend is viewed in the context of 400,000 years of climate data, the result is even more stark. Humans have profoundly changed the composition of Earth's atmosphere, and along with that, the energy balance of the planet.


This question is from the NASA quiz, It's a Gas. When the climate literacy quiz was originally written in 2018, the answer was 43%. NASA's original quiz was updated to reflect the continued addition of CO₂ to the atmosphere, which raised the percentage to 46%. This quiz was updated in 2021 to reflect yet another increase to 49%.

To keep up with the changing composition of the atmosphere, compare the current CO₂ concentration with the pre-industrial average of 278 ppm in 1750.

×

Show caption

Hide

Increases in concentrations of these gases since 1750 are due to human activities in the industrial era. Concentrations are parts per million (ppm) or parts per billion (ppb), indicating the number of molecules of the greenhouse gas per million or billion molecules of air. (Figure source: Forster et al.2007). Image from the National Climate Assessment. Source: [https://nca2014.globalchange.gov/highlights/report-findings/our-changing-climate]

Provenance: From the National Climate Assessment
Reuse: This item is in the public domain and maybe reused freely without restriction.

Climate Change: Atmospheric Carbon Dioxide from NOAA, Aug. 2020

Climate Change: How do we Know? from NASA

Our Changing Climate from the National Climate Assessment

×

Show caption

Hide

The trend in the globally averaged temperature shows that Earth's surface is rapidly warming. The graph shows average annual global temperatures since 1880 compared to the long-term average (1901-2000). Average temperature over land areas has warmed faster than ocean temperatures. For details and further explanation, visit the source: https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature This NOAA page is updated regularly.

Provenance: From NOAA
Reuse: This item is in the public domain and maybe reused freely without restriction.

As of mid 2021, the Earth's average temperature (considering both land and water) has risen 1.19 degrees Celsius (2.14 degrees F) over the pre-industrial average (1880-1900).

Furthermore, the rate of temperature change is increasing: "The global annual temperature has increased at an average rate of 0.07°C (0.13°F) per decade since 1880 and over twice that rate (+0.18°C / +0.32°F) since 1981." (Quote from the NOAA page linked below).

NOAA's page about global temperature provides a summary of changing temperatures; this page is updated regularly.

Sources

Climate Change: Global Temperature from NOAA (this page is updated regularly)

Global Temperature from NASA

Up-to-date temperature data and analysis from NASA's GISS Surface Temperature Analysis (GISTEMP v4)

×

Show caption

Hide

Temperature histories from paleoclimate data (green line) compared to the history based on modern instruments (blue line) suggest that global temperature is warmer now than it has been in the past 1,000 years, and possibly longer. (Graph adapted from Mann et al., 2008.) Image from NASA Earth Observatory. Source: https://earthobservatory.nasa.gov/Features/GlobalWarming/page3.php

Provenance: From NASA Earth Observatory
Reuse: This item is in the public domain and maybe reused freely without restriction.

We know that the Earth's temperature made big swings as we moved in and out of ice ages. And as rapid as those changes were, today we are warming the climate 10 times faster.

"As the Earth moved out of ice ages over the past million years, the global temperature rose a total of 4 to 7 degrees Celsius over about 5,000 years. In the past century alone, the temperature has climbed 0.7 degrees Celsius, roughly ten times faster than the average rate of ice-age-recovery warming."

"Models predict that Earth will warm between 2 and 6 degrees Celsius in the next century. When global warming has happened at various times in the past two million years, it has taken the planet about 5,000 years to warm 5 degrees. The predicted rate of warming for the next century is at least 20 times faster. This rate of change is extremely unusual." (From How is Today's Warming Different from the Past?)

"We know from past changes that ecosystems have responded to a few degrees of global temperature change over thousands of years," said Diffenbaugh. "But the unprecedented trajectory that we're on now is forcing that change to occur over decades. That's orders of magnitude faster, and we're already seeing that some species are challenged by that rate of change." (From Climate change on pace to occur 10 times faster than any change recorded in past 65 million years)

It's even more interesting to note past spikes in temperature in the paleoclimate record (such as the Paleocene-Eocene Thermal Maximum ~55 million years ago) have been associated with other extreme changes such as rapid ocean acidification which was detrimental to marine life on Earth. Also, the Permian Mass Extinction was thought to have been initiated by rapid ocean warming leading to reduction in circulation, oceans going anoxic and emission of poisonous hydrogen sulfide into the atmosphere. Earth's geologic history gives us plenty of evidence that rapid swings in climate cause difficult conditions for life.

Sources

How is Today's Warming Different from the Past? from NASA's Earth Observatory

Climate change on pace to occur 10 times faster than any change recorded in past 65 million years, Stanford scientists say from Stanford News

×

Show caption

Hide

The amount of solar energy received by the Earth has followed the Sun’s natural 11-year cycle of small ups and downs with no net increase since the 1950s. Over the same period, global temperature has risen markedly. It is therefore extremely unlikely that the Sun has caused the observed global temperature warming trend over the past half-century. Image from NASA.

Provenance: Image from NASA, from https://climate.nasa.gov/faq/14/is-the-sun-causing-global-warming/
Reuse: This item is in the public domain and maybe reused freely without restriction.

Sources

Why scientists think 100% of global warming is due to humans by CarbonBrief

Humans cause 93-123% of warming

Should the Earth be Cooling? from Skeptical Science

Pollen data shows humans reversed natural global cooling from the Guardian

×

The last time there was this much CO2 in the atmosphere, was the Pliocene, 3 million years ago. Image from NASA. Source: https://climate.nasa.gov/climate_resources/7/graphic-carbon-dioxide-hits-new-high/

Provenance: From NASA
Reuse: This item is in the public domain and maybe reused freely without restriction.

Throughout all of the cool-downs and warm-ups of the last ice ages, CO₂ never topped 300 ppm. So we're way above anything that happened during the ice ages. To look for the last time Earth's atmosphere had more than 400 ppm of CO₂ we have to go farther back. Way farther back, to the Pliocene, 3 to 5 million years ago.

How was the climate back then? The temperature was 2 to 4 degrees Celsius (3.6 to 7.2 degrees Fahrenheit) warmer than today, and sea level was 50 to 80 feet higher!

On the other hand, there were giant camels, so that part sounds pretty good.

Sources

CO2 Concentrations Hit Highest Levels in 3 Million Years - May, 2019

Atmospheric Carbon Dioxide from NOAA

What the Pliocene epoch can teach us about future warming on Earth from Science News

×

Show caption

Hide

Two ice cores from Antarctica. In the core in the foreground, gas bubbles are visible. The core in the background contains a volcanic ash layer. Photo by Karin Kirk.

Provenance: Karin Kirk, Freelance Science Writer and Geoscientist
Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

The science of paleoclimatology uses geologic evidence to determine what the climate was like throughout Earth's history. Learn more in the video, Our Shared Climate Future, by scientists at the University of Colorado, CIRES. This specific question is addressed at 2:40 in the 5-minute video.

Source


What is Paleoclimatology? from NOAA

The vast majority of climate scientists agree with the overwhelming evidence that humans are causing global warming. The reason there is a consensus of scientists is that there is a consensus of evidence.

×

This graphic summarizes the research on the scientific consensus on human-caused global warming. Each of these studies looked at expert opinion of climate scientists who have published peer-reviewed climate research or peer-reviewed climate papers. Image from Skeptical Science.

Provenance: Skeptical Science graphic, licensed under a Creative Commons Attribution 3.0 Unported License.
Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

The scientific consensus was measured by reading the abstracts of nearly 12,000 scientific papers. This exercise is easy for anyone to repeat: simply look at published papers in legitimate climate science journals, and tally up how many agree with the idea that humans are changing the climate. Or, if reading is not your thing, attend any earth science conference and listen to what scientists are saying. They are in resounding agreement – because the evidence is overwhelming.

If this is true, then why do we hear so much dissenting information? The answer is simple. Most of the claims that dismiss climate science are not based on legitimate science and are not found in peer-reviewed journals. When a paper has been peer-reviewed, that means it has been evaluated by a number of qualified scientists and found to have followed legitimate scientific methods (From the Consensus Project).

Source
s

Quantifying the consensus on anthropogenic global warming in the scientific literature

The Consensus Project

At the heart of this misconception is the idea that if something happens naturally, then it can only happen naturally. But of course that's not true. Here are some examples.

Forest fires occur naturally. Does that mean that arson is a hoax?

People die of natural causes. But sadly, people are sometimes murdered. But if people can die on their own does that mean that murder does not happen?

It rains, which makes my lawn wet. But sometimes, a sprinkler is used to make the lawn wet. So the lawn can become wet for either natural or human-caused reasons.

Rivers have always flooded. But some floods are either caused by, or made worse by human actions. If a dam ruptures, the resulting flood is because of humans – not because floods happen on their own.

Many processes on Earth have more than one cause. The presence of a natural cause does not negate the reality of a human trigger.

Furthermore, the fact that climate has changed on its own gives us some very helpful information. Throughout geologic history, we know that more greenhouse gases in the atmosphere equates to a warmer climate, regardless of the source of the greenhouse gases (from the ocean, from wildfires, from volcanoes, from melting permafrost, etc.). So as humans add CO₂ and other greenhouse gases to the atmosphere, we know that it also has the same warming effect. The physical process is the same either way.

Lastly, a key difference between past climate changes and today's climate change is the rate of change. Today's warming is much more rapid that past shifts in climate. This makes it harder for ecosystems to adapt.

In past geological ages the drivers of climate have been natural (volcanoes, plate tectonics, meteorites, cyanobacteria evolving and putting oxygen into our atmosphere, etc.), but now we as humans are the drivers of climate. This is why some scientists refer to today's geological era as the 'Anthropocene.' While it is scary to think that we as a species are responsible for altering the climate, it also highlights the fact that we humans are the first 'self-aware' climate driver and so could potentially do something about our actions.

Watch Katharine Hayhoe's lively explanation for this misconception:

While China is currently the largest emitter of greenhouse gases, cumulative emissions are an important way to look at our overall contribution to global warming.

China's greenhouse gas emissions per year have only recently surpassed the US. Over time, the USA has been the largest emitter of greenhouse gases to the atmosphere. In fact, we've emitted twice as much CO₂ as China.

This matters because greenhouse gases have a long life span in the atmosphere. CO₂ in the atmosphere lasts for 50 to 100 years or more (as explained in this article in Yale Climate Connections). The reason why it's so important to curb emissions quickly is because greenhouse gases have a long-lasting effect. It's also why we can't sit back and blame China for their high emissions. All nations need to work together to address climate change.

Sources

Our World in Data offers a particularly helpful discussion of greenhouse gas emissions from the USA, China, and other countries. (2017)

6 Graphs Explain the World's Top 10 Emitters from World Resources Institute, 2014

Interactive chart of top greenhouse gas emitters from World Resources Institute, 2017

List of Countries by CO2 Emissions - Wikipedia

As you know from the carbon cycle, some processes, like photosynthesis, use up carbon dioxide quickly, while others, like carbon dioxide captured by weathering of rocks, operate over many thousands of years. Thus, you can't put your finger on the exact life span of a given molecule of CO₂ in the atmosphere.

The bottom line is that once emitted, CO₂ continues to affect the climate for decades to millennia. That's why reducing emissions quickly is important. Because of the existing CO₂ in the atmosphere, the Earth will continue to warm even after we stop burning fossil fuels.

The complexity of CO₂ residence time is summed by Zeke Hausfather in Yale Climate Connections:

"Using a combination of various methods, researchers have estimated that about 50 percent of the net anthropogenic pulse would be absorbed in the first 50 years, and about 70 percent in the first 100 years. Absorption by sinks slows dramatically after that, with an additional 10 percent or so being removed after 300 years and the remaining 20 percent lasting tens if not hundreds of thousands of years before being removed."

IPCC uses an estimate of 5 to 200 years, noting, "No single lifetime can be defined for CO₂ because of the different rates of uptake by different removal processes."

Sources

Common Climate Misconceptions: Atmospheric Carbon Dioxide from Yale Climate Connections

Attributes of Greenhouse Gases from IPCC

CO2 emissions change our atmosphere for centuries

The science is evolving on this question, and this quiz was updated in 2021 to reflect those changes. Among all the bad news on climate change, this is a bit of good news. There is general agreement among scientists that when emissions fall to net zero, then the amount of greenhouse gases in the atmosphere will stop increasing. At that point, the global increase in temperature will slow or stop.

Carbon Brief has an excellent, well-referenced article that explains why the science - and the messaging - around this topic has changed.

There are a few factors to keep in mind:

• Air pollution - caused largely by burning fossil fuels - actually cools the planet by reflecting some incoming solar radiation. It's likely that there would be a temporary increase in temperature if airborne pollution were stopped. Overall, reducing air pollution would save millions of lives and trillions of dollars, so the benefit is still very worthwhile.
• Often, the differing messaging on this topic is due to different questions being posed. For example, Earth's temperatures should stop increasing when greenhouse gases stop increasing, but an actual cool-down could take longer because of the long residence time of greenhouse gases in the atmosphere.

This remains an active area of climate research.

• There is an annual 'wiggle' in the amount of CO₂ in the atmosphere.
• There is also an overall trend of increasing CO₂ in the atmosphere.

Go on to the next question to learn more about this data and what it means.

This data is from Scripps, and current CO₂ data and many other forms of atmospheric CO₂ data are available from the website and from the related Keeling curve website.

The 'seesaw' of carbon dioxide in the atmosphere is caused by the changing seasons. During the summer in the Northern Hemisphere, plants and marine algae take up CO₂ through photosynthesis. As plants use up CO₂, it's temporarily drawn down from the CO₂ in the atmosphere. In the fall, plants slow down their uptake of CO₂, and CO₂ is released from soils. This process is dominated by the Northern Hemisphere because there is more land mass in the Northern Hemisphere.

×

Show caption

Hide

The lower graph shows carbon released from burning fossil fuels and other sources. The upper graph shows the accumulation of CO2 in the atmosphere over the same time scale. Image by Robert A. Rohde for Global Warming Art

Provenance: From Wikimedia Commons, by Robert A. Rohde for Global Warming Art.
Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

The evidence is absolutely clear on this one. Humans have burned ever-increasing amounts of fossil fuels since the industrial revolution. Over this same time scale, CO₂ concentrations in the atmosphere have risen similarly. Isotope studies show the excess carbon in the atmosphere is plant-based carbon that had been locked away in Earth's crust until recently. If the increase in CO₂ were coming from the oceans or melting permafrost, it would have a different isotopic signature.

That said, warming oceans and melting permafrost also release CO₂. These are examples of self-reinforcing cycles, also known as a positive feedback cycles. But the oceans are warming and permafrost is thawing because of human emissions of greenhouse gases. They are not driving the cycle, they are responding to changes caused by humans.

Sources

How do we know that recent CO2 increases are due to human activities?

Is the Current Rise in CO2 Definitely Caused by Human Activities? (answer: yes!) Response written by geochemist Ralph Keeling

Current CO₂ readings, updated daily

History of atmospheric carbon dioxide from 800,000 years ago until January, 2016 - an intriguing visualization

Keeling curve video from Scripps

×

Show caption

Hide

Observed sea level since the start of the satellite altimeter record in 1993 (black line), plus independent estimates of the different contributions to sea level rise: thermal expansion (red) and added water, mostly due to glacier melt (blue). Added together (purple line), these separate estimates match the observed sea level very well. NOAA Climate.gov graphic, adapted from Figure 3.15a in State of the Climate in 2016.

Provenance: From NOAA, State of the Climate 2016
Reuse: This item is in the public domain and maybe reused freely without restriction.

From NOAA Climate.gov:

"Sea level is rising for two main reasons: glaciers and ice sheets are melting and adding water to the ocean and the volume of the ocean is expanding as the water warms. A third, much smaller contributor to sea level rise is a decline in water storage on land—aquifers, lakes and reservoirs, rivers, soil moisture—mostly as a result of groundwater pumping, which has shifted water from aquifers to the ocean.

"From the 1970s up through the last decade, melting and thermal expansion were contributing roughly equally to the observed sea level rise. But the melting of glaciers and ice sheets has accelerated, and over the past decade, the amount of sea level rise due to melting—with a small addition from groundwater transfer and other water storage shifts—has been nearly twice the amount of sea level rise due to thermal expansion."

Sources

Climate Change: Global Sea Level from NOAA Climate.gov

Is Sea Level Rising? from NOAA National Ocean Service

×

The Chemistry of Ocean Acidification

Provenance: National Resource Council of the National Academies
Reuse: This item is in the public domain and maybe reused freely without restriction.

Ocean acidification is sometimes called "the other carbon dioxide problem." The oceans have absorbed 25 to 30 percent of the CO₂ released into the atmosphere.

The increase in dissolved CO₂ makes the ocean water more acidic (lowering the pH). This matters because many organisms in the ocean – from coral reefs to clam shells to plankton – build shells from calcium carbonate that is dissolved in ocean water. More acidic water makes it harder for these animals to build and maintain their shells.

Since the industrial revolution, the pH of seawater has fallen from 8.2 to 8.1 – a decrease of 0.1 pH units. While that may not sound like much, it's a 30% increase in acidity. It's also important to note that the oceans are not acidic overall. The pH of ocean water is above 7, which is means it's basic, not acidic. But ocean acidification is making the water less basic – - or more acidic. For many organisms, this is a dramatic change in the conditions they are adapted for. The current drop in pH is the fastest known change in ocean chemistry in the past 50 million years. (Reference)

Why does this matter? From NOAA's ocean acidification education page:

"Ocean acidification is currently affecting the entire world's oceans, including coastal estuaries and waterways. Today, more than a billion people worldwide rely on food from the ocean as their primary source of protein. Approximately 20% of the world's population derives at least 1/5 of its animal protein intake from fish. Many jobs and economies in the U.S. and around the world depend on the fish and shellfish that live in the ocean."

Sources

Ocean Acidification from NOAA

What is Ocean Acidification from NOAA

Ocean Acidification from the Smithsonian

×

Bleached branching coral in foreground with healthy coral beyond, Great Barrier Reef, Australia.

Provenance: Ginny Brown, National Council for Science and the Environment
Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

From NOAA's National Ocean Service page:

"Warmer water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching. When a coral bleaches, it is not dead. Corals can survive a bleaching event, but they are under more stress and are subject to mortality."

"A healthy, resilient reef can either resist a stressful event, like bleaching, or recover from it. When a coral bleaches, it is not dead. Corals can survive if water temperatures return to normal quickly."

Source

What is Coral Bleaching? from NOAA

Switching energy sources away from fossil fuels, wasting lass food, and adopting a plant-based diet, and restoring tropical forests are all key solutions for limiting climate change. Educating girls and family planning are is another solution that can reduce greenhouse gas emissions.

See the full list of solutions from Project Drawdown. This list is continuously updated, and this quiz question was updated in 2021 and is subject to change as we learn more.

Large-scale, systemic change is needed to address climate change, and changes made on a personal level are not enough to solve the problem. Nonetheless, adopting a cleaner lifestyle offers the simultaneous benefits of emitting fewer greenhouse gases while also illustrating the scale and effectiveness of various solutions. These CLEAN resources involve reductions in personal energy use:

The Lifestyle Project (more info)

How Much Energy is on My Plate? (more info)

Source

Project Drawdown – Solutions

×

Show caption

Hide

Three scenarios showing the amount that emissions need to decline in order to stay below the 2 degree (C) threshold. The later we wait to seriously curb greenhouse gas emissions, the steeper the decline needs to be. Another way of looking at this is the sooner we start, the more time we have to accomplish the necessary amount of reductions. Image courtesy of Stefan Rahmstorf 2017. Source: [link https://www.nature.com/news/three-years-to-safeguard-our-climate-1.22201 'Three years to safeguard our climate'], Nature, June 2017

Provenance: NEED PERMISSION
Reuse: If you wish to use this item outside this site in ways that exceed fair use (see http://fairuse.stanford.edu/) you must seek permission from its creator.

This quiz question was written in 2018. The 'deadline' of 2020 has come and gone, so we can observe our progress on reducing emissions. The world consumed less fossil fuels in 2020, and less energy overall, largely due to the Covid-19 pandemic. So far in 2021, it appears that consumption is rebounding past 2020 levels. If we intend to minimize dramatic effects on Earth's climate system, we face a monumental challenge to overhaul the world's energy use within just a few years.

Note that there are other factors that can influence this estimate, such as CO₂ removal from the atmosphere. The degree to which direct carbon capture could reduce the buildup of atmospheric greenhouse gases remains speculative at this point.

In 2017 Rahmstorf and Levermann concluded, "It is still possible therefore to meet the Paris temperature goals if emissions peak by 2020 at the latest.... We will need an enormous amount of action and scaled up ambition to harness the current momentum in order to travel down the decarbonisation curve at the necessary pace; the window to do that is still open."

Since the statement above was made, emissions have risen, fallen, then risen again.

Sources

BP Statistical Review of Energy 2020 | Self-updating graphs showing annual trends in energy use.

Why global emissions must peak by 2020

1.5C climate target slipping out of reach - by CarbonBrief

Emissions Gap Report 2019 - Interactive report with excellent graphics, by the UN Environment Programme