STEP 1: Problem Identification
If we focus on climate change as the problem, the key driver is accumulating CO2 emissions that keep pushing atmospheric concentrations higher.
"Cumulative emissions of CO2 largely determine global mean surface warming by the late 21st century and beyond. Projections of greenhouse gas emissions vary over a wide range, depending on both socio-economic development and climate policy."
~ IPCC (2014, p. 8)
CO2.Earth brings focus to the critical problem of 'rising CO2.' It also situates this problem among a broader array global environmental problems. This broader context is provided by content related to the Annual Greenhouse Gas Index, "The Great Acceleration" (see "The GA" tab on this page) and Planetary Boundaries. Each problem appears to identify a problem in the relationship between humankind and the earth system. Learning about the problems may offer an opportunity to improve our collective relationship with the earth.
This "problem identification" sets out some of the dimensions of the climate and other global environmental problems. It offers a starting place to answer questions like these:
- 'What problem or problems exist?
- "What are the risks?
- How do we know these things?
IPCC Assessment Reports
The Intergovernmental Panel on Climate Change (IPCC) has given government policy makers the most authoritative and objective scientific and technical assesments of changes to earth's climate system. The reports it publishes are the product of work by thousands of experts and scientists around the world who represent a wide range of views and disciplines.
The following excerpt summarizes the 2014 Synthesis Report (SYR) in one paragraph.
The SYR confirms that human influence on the climate system is clear and growing, with impacts observed across all continents and oceans. Many of the observed changes since the 1950s are unprecedented over decades to millennia. The IPCC is now 95 percent certain that humans are the main cause of current global warming. In addition, the SYR finds that the more human activities disrupt the climate, the greater the risks of severe, pervasive and irreversible impacts for people and ecosystems, and long-lasting changes in all components of the climate system. The SYR highlights that we have the means to limit climate change and its risks, with many solutions that allow for continued economic and human development. However, stabilizing temperature increase to below 2°C relative to pre-industrial levels will require an urgent and fundamental departure from business as usual. Moreover, the longer we wait to take action, the more it will cost and the greater the technological, economic, social and institutional challenges we will face.
Link
IPCC 2013 Press Release (2013) Human influence on climate clear
Reference
IPCC. (2014). Climate change 2014: Synthesis report. Contribution of working groups I, II and III to the fifth assessment report of the Intergovernmental Panel on Climate Change. (Core Writing Team, R. K. Pachauri, & L. A. Meyer Eds.). Geneva, Switzerland: IPCC. [web + .pdf + Chinese + Korean]
The Great Acceleration
Source image IGBP Great Acceleration (high res.; full image)
"The second half of the twentieth century is unique in the entire history of human existence on Earth. Many human activities reached take-off points sometime in the twentieth century and have accelerated sharply towards the end of the century. The last 50 years have without doubt seen the most rapid transformation of the human relationship with the natural world in the history of humankind."
~ Will Steffen et al. (2004, p. 131)
Rising CO2 is a critical disturbance that humans are making in the biosphere. But it's not the only one.
The start of the Industrial Revolution is often referenced as the point when our speicies begain to exert notable pressure on the functionning of the earth system. A lot has changed since the late 1700s when James Watt brought steam engines into the world.
Early in the 21st Century, researchers at the International Geosphere-Biosphere Programme (IGBP) in Sweden set out to record a trajectory of the 'human enterprise' in recent centuries. They chose 12 indicators that tracked changes in the human enterprise, and 12 that tracked changes in the function and structure of natural systems. They wanted "to build a more systematic picture of the human-driven changes to the earth system" (Steffen et al., 2015, p. 2). To their surprise, they found a "dramatic change in magnitude and rate of the human imprint from about 1950 onwards" (p. 2).
This was not news among historians, but not generally recognized among earth system scientsts. Nonetheless, scientists consolidated and quantified the changes. They aimed "to capture the holistic, comprehensive and interlinked nature of the post-1950 changes simultaneously sweeping across the socio-economic and biophysical spheres of the earth system, encompassing far more than climate change" (p. 2).
Below, you can see latest charts for indicators the IGBP posted in January 2015.
24 'Great Acceleration' Indicators
Planetary Dashboard | IGBP
Will Steffen and his research team report that "The Great Acceleration" was first used in 2005 at a workshop in Berlin after the publication of the 24 planetary indicators. The quote below is taken from the workshop report.
"The “engine” of the Great Acceleration is an interlinked system consisting of population increase, rising consumption, abundant energy, and liberalizing political economies. Globalization, especially an exploding knowledge base and rapidly expanding connectivity and information flow, acts as a strong accelerator of the system. The environmental effects of the Great Acceleration are clearly visible at the global scale: changing atmospheric chemistry and climate, degradation of many ecosystem services (e.g., provision of freshwater, biological diversity), and homogenization of the biotic fabric of the planet. The Great Acceleration is arguably the most profound and rapid shift in the human–environment relationship that the Earth has experienced."
~ Charles Redman et al. (2007, p. 131)
Links
IGBP Great Acceleration
IGBP Press Release (2015) Planetary dashboard shows "Great Acceleration"
IGBP POWERPOINT (2015) Great Acceleration (21 MB)
IGBP Great acceleration data [Excel 2007]
IGBP + YouTube VIDEO (2014) Welcome to the Anthropocene
Related
Critical Angle Skuce (2015) The history of emissions and TGA
NY Times Revkin (2015) Can humanity's 'Great Acceleration' be managed?
References
Costanza, R., van der Leeuw, S., Hibbard, K., Aulenbach, S., Brewer, S., Burek, M., . . . Steffen, W. (2012). Developing an integrated history and future of people on earth (IHOPE). Current Opinion in Environmental Sustainability, 4(1), 106-114. doi:10.1016/j.cosust.2012.01.010 [COES + researchgate .pdf]
Redman, C., Crumley, C. L., Hassan, F. A., Hole, F., Morais, J., Riedel, F., . . . Yasuda, Y. (2007). Group report: Millennial perspectives on the dynamic interaction of climate, people, and resources. In R. Costanza, L. Graumlich, & W. Steffen (Eds.), Sustainability or Collapse? 96th Dahlem Workshop on Integrated History and Future of People on Earth (IHOPE) (pp. 115-148). Cambridge, MA: The MIT Press and Freie Universität Berlin. [MIT]
Steffen, W., Broadgate, W., Deutsch, L., Gaffney, O., & Ludwig, C. (2015). The trajectory of the Anthropocene: The Great Acceleration. The Anthropocene Review. doi:10.1177/2053019614564785 [ANR]
Steffen, W., Sanderson, R. A., Tyson, P. D., Jäger, J., Matson, P. A., Moore III, B., . . . Turner, B. L. (2004). Global change and the earth system: A planet under pressure. Berlin: Springer Science & Business Media. [IGBP + .pdf book]
Factors (detection & attribution)
"Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, and in global mean sea level rise; and it is extremely likely to have been the dominant cause of the observed warming since the mid-20th century. In recent decades, changes in climate have caused impacts on natural and human systems on all continents and across the oceans."
~ IPCC (2014, p. 47)
The earth system is large, complex and dynamic. Detecting planetary changes and attributing causes requires collaboration among many skilled researchers who make many kinds of observations and use many kinds of instruments and plus computer models to expand knowosed about the earth sytem.
Individuals are learning within a cooperative context. Consider Dave Keeling as an example of an individual scientist. Keeling is well known for starting the longest-running instrument record for CO2 measurements at the Mauna Loa Observatory, 3400 metres above sea level. The first monthly average he reported, 315.71 parts per million for March 1958, remains an important datapoint that is still incorporated into studies and models by scientists today. Over time and around the world, this kind of earth monitoring work ultimately forms the basis for what scientists know about the earth system and how it behaves.
There are perhaps many ways of learning how earth system scientists learn what they know about the earth system. To explore these issues further, consider looking into the use of quantitative statistics for detection and attribution of factors contributing to climate changes. And consider looking into modelling methods scientists use to test and expand knowledge about the earth system.
Related
NASA GISS 2015 Accounting for climate's backseat drivers
NASA GISS Simple climate model for high school classrooms
RealClimate The CO2 problem in 6 easy steps
Climate Forcings
Forcings are factors outside the climate system that force or drive changes to the climate system. This essentially means that a measurable external change is forcing a change in average temperatures, either warmer or cooler.
Forcings can be natural, such as changes in energy output from the sun. And they can be caused by humans, such as changes in atmospheric concentrations of heat-trapping gases, especially carbon dioxide and methane. The chart below shows changes in different forcings since 1880.
Source graphic NASA GISS
Links
NASA GISS Forcings in GISS climate model
OSS Climate forcing
NOAA Paleoclimatology What are climate forcings?
Impacts
"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."
~ IPCC (2014, p. 47)
As certain human activities continue to drive multiple changes in the earth system, we may expect impacts that cascade and worsen the longer we continue the activities that warm, acidify and degrade the biosphere. Because human institutions have not committed to a plan that will stabilize the concentraion of greenhouse gases in the atmosphere, we don't know the extent of future global changes. This signficantly reduces certainty of a stabilized future.
To be blunt about the situation, the following perspective comes from Professor Kevin Anderson, Deputy Director of the Tyndall Centre for Climate Change Research.
"We are in ‘injury time’ for 2°C – and things are not looking good. However, time will continue regardless even if we blow the 2°C carbon budgets, we still need to drive even harder for deep and rapid mitigation alongside preparing for the regional impacts of a 4, 5 or even 6°C future. But we must note that adaptation to such a future scenario will never be sufficient for the many millions who will suffer and die as a consequence of the fossil fuelled hedonism enjoyed by relatively few of us – including me and very likely anyone reading this; we are the high emitters who have explicitly chosen not to care."
~ Kevin Anderson [See Páll Ormarsson (2015)]
The IPCC made a statement that seems scientifically compatible, but the tone is less personalized.
"Without additional mitigation efforts beyond those in place today, and even with adaptation, warming by the end of the 21st century will lead to high to very high risk of severe, widespread and irreversible impacts globally."
~ IPCC (2014, p. 18)
Nature and Extent of Impacts
Accumulating evidence from a variety of past crises suggests that humanity may be moving increasingly toward a future marked by multiple global and interconnected risks. When a risk to a financial, social or ecological system materializes as a crisis, the changes are sometimes non-linear, abrupt, surprising and even irreversible. Such crises are often triggered by a mix of interacting social, environmental and technological factors. [See Galaz et al. (2011)]
To see examples of social and economic impacts at CO2.Earth, jump to the page about people and communities on the front lines of global climate change.
Below, a list of links has been started for scientific data, indexes and images that show the types of changes that are happening worldwide on land and in the oceans. To begin, the following graphic is updated each day to show cumulative days of ice melt in Greenland.
Greenland Ice Melt YTD
Greenland Ice Sheet Today | NSIDC
Source Image NSIDC Greenland Ice Sheet Today [high resolution .png]
Data Links
Ice Sheets
NSIDC Ice sheets database records
Snow
NSIDC Snow database records
Permafrost
NSIDC Permafrost database records
Soil Moisture
NSIDC Soil moisture database records
NOAA NCEI Crop moisture stress index (CMSI)
Glaciers
NSIDC Glacier database records
NSIDC Glacier photo database (since 1880) [search]
NSIDC Antarctic Glaciological Data Center
Sea Ice
NSIDC Sea ice index [web graphics + data portal)
NSIDC Daily sea ice extent--Northern Hemisphere
NSIDC Arctic sea ice news & analysis
Sea Level
CSIRO Sea level data [GTh sea level + global ocean heat content]
Arctic Change
NSIDC Satellite observations of arctic change
ELOKA Exchane for local observations and knowledge of the arctic
More Data Sets
NOAA-NCEI Societal Impacts
NOAA-NCEI Extremes (North America & USA)
NOAA-NCEI Snow and Ice Data (Global & USA)
NOAA-NCEI Teleconnections: Variability in atmospheric circulation
IGBP 2011 Climate Change Index
Other Data Portals
NSIDC & Google Earth NSIDC data (KML files) for Google Earth
NASA EOSDIS Earth data website [search portal]
NASA Earth Observatory website
References
Folke, C., Jansson, Å., Rockström, J., Olsson, P., Carpenter, S. R., Chapin, F. S., . . . Westley, F. (2011). Reconnecting to the biosphere. AMBIO, 40(7), 719-738. doi:10.1007/s13280-011-0184-y
Galaz, V., Galafassi, D., Tallberg, J., Boin, A., Hey, E., Ituarte-Lima, C., . . . Westley, F. (2014). Connected Risks, Connected Solutions. Stockholm: Stockholm Resilience Centre, Stockholm University, and the Global Challenges Foundation. Retrieved from http://www.changingplanet.se/connected-risks. [web]
IPCC. (2014). Climate change 2014: Synthesis report. Contribution of working groups I, II and III to the fifth assessment report of the Intergovernmental Panel on Climate Change. (Core Writing Team, R. K. Pachauri, & L. A. Meyer Eds.). Geneva, Switzerland: IPCC. [web + .pdf + Chinese + Korean]
Páll Ormarsson, O. (2015, October 20). Arctic 2015: Things are not looking good! Iceland Monitor. Retrieved from http://icelandmonitor.mbl.is/news/nature_and_travel/2015/10/17/arctic_2015_things_are_not_looking_good/ [web]
CO2 Stabilization Prerequisites
Reposted from ScienceDaily (Feb. 18, 2008) Now that scientists have reached a consensus that carbon dioxide emissions from human activities are the major cause of global warming, the next question is: How can we stop it? Can we just cut back on carbon, or do we need to go cold turkey? According to a new study by scientists at the Carnegie Institution, halfway measures won’t do the job. To stabilize our planet’s climate, we need to find ways to kick the carbon habit altogether.
In the study, to be published in Geophysical Research Letters, climate scientists Ken Caldeira and Damon Matthews used an Earth system model at the Carnegie Institution’s Department of Global Ecology to simulate the response of the Earth’s climate to different levels of carbon dioxide emission over the next 500 years. The model, a sophisticated computer program developed at the University of Victoria, Canada, takes into account the flow of heat between the atmosphere and oceans, as well as other factors such as the uptake of carbon dioxide by land vegetation, in its calculations.
This is the first peer-reviewed study to investigate what level of carbon dioxide emission would be needed to prevent further warming of our planet.
“Most scientific and policy discussions about avoiding climate change have centered on what emissions would be needed to stabilize greenhouse gases in the atmosphere,” says Caldeira. “But stabilizing greenhouse gases does not equate to a stable climate. We studied what emissions would be needed to stabilize climate in the foreseeable future.”
The scientists investigated how much climate changes as a result of each individual emission of carbon dioxide, and found that each increment of emission leads to another increment of warming. So, if we want to avoid additional warming, we need to avoid additional emissions.
With emissions set to zero in the simulations, the level of carbon dioxide in the atmosphere slowly fell as carbon “sinks” such as the oceans and land vegetation absorbed the gas. Surprisingly, however, the model predicted that global temperatures would remain high for at least 500 years after carbon dioxide emissions ceased.
Just as an iron skillet will stay hot and keep cooking after the stove burner’s turned off, heat held in the oceans will keep the climate warm even as the heating effect of greenhouse gases diminishes. Adding more greenhouse gases, even at a rate lower than today, would worsen the situation and the effects would persist for centuries.
"What if we were to discover tomorrow that a climate catastrophe was imminent if our planet warmed any further? To reduce emissions enough to avoid this catastrophe, we would have to cut them close to zero — and right away," says Caldeira.
Global carbon dioxide emissions and atmospheric carbon dioxide concentrations are both growing at record rates. Even if we could freeze emissions at today’s levels, atmospheric carbon dioxide concentrations would continue to increase. If we could stabilize atmospheric carbon dioxide concentrations, which would require deep cuts in emissions, the Earth would continue heating up. Matthews and Caldeira found that to prevent the Earth from heating further, carbon dioxide emissions would, effectively, need to be eliminated.
While eliminating carbon dioxide emissions may seem like a radical idea, Caldeira sees it as a feasible goal. “It is just not that hard to solve the technological challenges,” he says. “We can develop and deploy wind turbines, electric cars, and so on, and live well without damaging the environment. The future can be better than the present, but we have to take steps to start kicking the CO2 habit now, so we won't need to go cold turkey later.”
Journal reference: Matthews, H. D., and K. Caldeira (2008), Stabilizing climate requires near-zero emissions, Geophysical Research Letters, doi:10.1029/2007GL032388, in press.
Precaution.org | Stabilizing climate requires near-zero emissions
AGU.org | ABSTRACT: Stabilizing climate requires near-zero emissions
COP 21 | 2015 Paris Climate Talks
Image The Climate Group 2014 / Flickr / cc-by-nc-sa 2.0
Downloaded from climaterealityproject.org
"I don't know that it is possible to say right now are we going to end up with 1.5, 1.6, 1.7, 1.8, 1.9°C? But it's got to be within that range. There is no doubt that it has to be below 2°C."
...
"It’s very obvious that lower temperatures provide more security and more safety. That is unquestioned."
~ Christiana Figueres, Executive Secretary, UNFCCC [See Hickman (2015, June)]
The United Nations climate conference in Paris, France (November 30 - December 11, 2015) went one day extra to reach a deal.
UNFCCC 195 Nations Set Path to Keep Temperature Rise Well Below 2 Degrees Celsius
UNFCCC Paris climate change conference 2015
UNFCC Paris Agreement: Library Webpage + Agreement .pdf
Tabs below connect you to resources that are relevant for understanding the Paris conference and the outcomes.
COP 26 | 2021 Glasgow UNFCCC Conference of the Parties
Image @UNFCCC Twitter posted 2021-10-14
Tabs below connect you to resources that are relevant for understanding the COP26 UN Climate Summit held in Glasgow from November 1 - 12, 2021.
Glasgow Climate Pact
Excerpts from the CarbonBrief analysis of November 15, 2021:
The surprise package at COP26 was the adoption of a “Glasgow Climate Pact”, an unprecedented, lengthy and wide-ranging political decision towards a more ambitious climate response.
This text “requests” that countries “revisit and strengthen” their climate pledges by the end of 2022, calls for a “phasedown” of coal and sets up processes towards delivering a global goal on adaptation, higher levels of climate finance and finance for loss and damage.
Although the text left many disappointed over a lack of “balance” between the strength of language and action on emissions cuts, relative to finance or loss and damage, the fact that it was agreed at all is a relative novelty for the COP process.
...there is a marked shift in the language – and specitivity – that countries were collectively willing to sign off in Glasgow, compared with earlier summits.
The Glasgow text puts the IPCC’s findings front and centre, under the first subheading “science and urgency”. It “recognises” that the impacts of climate change will be “much lower” at 1.5C compared with 2C and “resolves to pursue efforts” to stay under the lower limit.
This puts a slightly stronger emphasis on 1.5C, with the Paris text itself having only said countries would “pursu[e] efforts” to stay below that rise in global temperature.
The pact then reiterates the IPCC special report finding that limiting warming to 1.5C requires “rapid, deep and sustained” emissions cuts, with carbon dioxide (CO2) emissions falling to 45% below 2010 levels by 2030 and to net-zero around mid-century.
(Note paragraph 22 refers to the 1.5C limit in general, whereas an earlier draft of the text had talked of staying below that level “by 2100”, implying potential temperature “overshoot”. Some climate scientists had expressed concern about this draft wording.)
The pact “welcomes” the latest IPCC report and “expresses alarm and utmost concern” at warming having already reached 1.1C, with remaining carbon budgets now “small and being rapidly depleted”.
It “notes with serious concern” that current pledges will see emissions increase by 2030 and starts a work programme on faster cuts “in this critical decade”, with a report due at COP27 next year.
It also starts an annual ministerial meeting on “pre-2030 ambition”, with the first at COP27.
The pact then “requests” that countries “revisit and strengthen” their targets by the end of 2022 “as necessary to align with the Paris Agreement temperature goal…taking into account different national circumstances”.
This language mirrors the wording in the Paris decision text, which “request[ed]” countries improve their pledges by 2020. It also gives a nod to those developing countries that wanted to emphasise the need for rich nations – or major emitters – to take the lead.
Despite some initial confusion, the “request” to ratchet ambition in 2022 is also stronger wording than in earlier drafts, which had merely “urge[d]” parties to step up next year.
Throughout COP26, many parties and observers called for this tightening of “ambition”. Ultimately, this “request” is likely to be ignored by some countries in 2022, in the same way that around 40 countries failed to offer new or updated NDCs before COP26. Nevertheless, the wording sets a clear expectation that all countries will raise their game next year, with intense diplomatic pressure likely to fall on those that refuse to play ball.
Again, this goes beyond what was agreed in Paris, where countries were only expected to update their pledges every five years – with an option to do so at any time. The rationale for this is clear. The next round of NDCs are due to cover the period from 2031 onwards, yet a yawning gap remains between current pledges to 2030 and the 1.5C limit.
The pact’s new request to revisit and strengthen 2030 targets next year therefore offers a narrow window through which the 1.5C limit could be kept within reach.
In addition, the Glasgow pact “urges” those that have yet to update their NDCs to do so “as soon as possible” and requests the UN climate body to publish annual updates to its synthesis report, on the combined climate impact of countries’ NDCs.
Similarly, it “urges” those that have not yet submitted long-term strategies to the UN to do so before COP27 “towards just transitions to net-zero emissions by or around mid-century”.
"COP Curve" Chart: Adapted by CO2.Earth from a carboncredits.com graphic.
COP26 Outcomes
CarbonBrief 2021 Key outcomes agreed at the UN climate talks in Glasgow
COP26 Primer
Guardian What is COP26 and why does it matter? A complete guide
2021 Conference Links & Info
UK COP26 Home
UK COP26 COP26 explained
UK COP26 Public access to the Green Zone climate action activities in Glasgow
UK COP26 Domestic leadership in the UK
UK COP26. News
UK COP26 Negotiations
UNFCCC Info for COP26 participants
UNFCCC Latest info on COP26
The Indian Express (Aug 2021) Explained: COP26 climate conference & why it is important
Climatenexus (web). COP26: Issues and expected storylines
WHO (Oct 2021) COP26 special report on climate change and health
World Resources Institute (Sep 2021) What vulnerable countries need from COP26 summit
World Economic Forum (Aug 2021) 6 key takeaways from new UN climate change report
Numbers for Determining COP26 Progress
Climate Action Tracker (ongoing upda tes) Climate Target Update Tracker
Carbon Tracker Home page (Carbon Tracker @COP26)
UNFCCC (Sep 2021 release) National Emissions Synthesis Report: Big concern, some progress
UNFCCC (web) Nationally determined contributions
UNFCCC (web) All about the NDCs
Global Climate & Health Alliance (Sep 2021) Health NDCs Scorecard
Climate Action Tracker (ongoing updates) Countries without improved climate ambition
Key UN Climate Reports
2021: IPCC AR6 Climate Report
IPCC (2021) AR6 Climate Change 2021: The Physical Science Basis
Climate Home News (Aug 2021) Five takeaways from the IPCC 2021 climate science report
Reuters Events (Sep 2021) Hopes for success at COP26 dim despite alarm raised by IPCC
European Academies Science Advisory Council (Aug 2021) Key messages for UNFCCC COP26
International Chamber of Commerce (Aug 2021). Code red warning from IPCC must translate into action
2020: UNEP Emissions Gap Report
UNEP (Dec 2020) Emissions Gap Report 2021
Mock COP26
Mock COP26 was an international, virtual climate change conference held for two weeks starting November 19, 2020.
Mock COP26 Our Treaty: 18 policies voted for by delegations of more than 140 countries
Guardian (Dec 2020) Mock COP26 activisits vote on treaty ahead of 2021 climate summit
BBC (Nov 2020) What is Mock COP26 all about?
UK COP26 (Sep 2021) What does meaningful youth leadership look like?
Praxis Research / Cabot Institute (2020) Download Mock COP Resources
STEP 4: World Engagement
To address the global environmental problems that our species and planet faces, the world needs to be engaged. All of humanity needs to be engaged. National governments are engaged.
196 countries
195 Parties to the Convention
Nature 2005 Kyoto Protocol comes into force
7 Billion People
Non-Governmental Organizations
Markets
STEP 5: World Targets
The world has an ultimate objective to avoid dangerous interference with the climate system. Prior pages cover some climate system basics and forums to engage for learning, responding and innovating solutions. What's missing? What's still needed? We need to quantify a target and put date on it. As with anything, this can generate focus and energy among diverse individuals and groups to move quickly toward an outcome that is widely seen as desirable and important.
For climate change, world institutions, UNFCCC member states in particular, have indicated strong support for a measurable target (avoid 2°C) and a date (now and forever). On the other side of the coin, the temperature trajectory is powerful and will exceed 2°C if sufficient changes in human activities are not implemented soon enough.
Here, 'Stabilization Step 5' takes a step back to introduce the 'avoid 2°C' target, other temperature targets and some other types of targets. Whether or not 'avoid 2°C' maintains the wide support it has now, it may help to move forward with eyes wide open. Further, multiple targets may be complementary and useful.
Carbon Budgets
A carbon budget quantifies remaining CO2 or greenhouse gas (CO2 equivalent) emissions that may occur before breaching a guardrail target like 'avoid 1.5°C' or 'avoid 450 ppm CO2'. Adopting a cumulative carbon budget reflects a choice to cease emissions before a particular guardrail is reached.
CO2 persists in the atmosphere for periods of time that exceed multiple human lifetimes. Thus, carbon budgets are cumulative over a period of centuries or millenia. They are not reset each year like many financial budgets.
References
Meinshausen et al. (2009). Greenhouse-gas emission targets for limiting global
warming to 2C. Nature, 458 1158-1163. [.pdf + resources]
Zickfeld, K., Eby, M., Matthews, H. D., Weaver, A. J., & Schellnhuber, H. J. (2009). Setting cumulative emissions targets to reduce the risk of dangerous climate change. Proceedings of the National Academy of Sciences of the United States of America, 106(38), 16129-16134. [abstract + .pdf]
2°C Guardrail
Paris Climate Talks: The 2°C Limit
Nature video examines the science behind the warming target
Source: Nature | November 19, 2015
Tracking Temperature
CO2.earth Global warming update
Related
FiveThirtyEight '16 When will it actually be hotter than 2 degrees?
Carbon Brief '14 Two degrees: Will we avoid dangerous climate change?
Carbon Brief '14 Two degrees: History of the climate change limit
Pathways to 2°C
"There are multiple mitigation pathways that are likely to limit warming to below 2°C relative to pre-industrial levels. These pathways would require substantial emissions reductions over the next few decades and near zero emissions of CO2 and other long-lived greenhouse gases by the end of the century. Implementing such reductions poses substantial technological, economic, social and institutional challenges, which increase with delays in additional mitigation and if key technologies are not available. Limiting warming to lower or higher levels involves similar challenges but on different timescales."
~ IPCC (2014, p. 20)
"UN negotiations on climate change aim to limit warming to 2 °C above pre-industrial temperatures. There is, however, no agreement on how to define pre-industrial temperature."
~ New Scientist, 2015 (attributed to Ed Hawkins, University of Reading, UK)
