Future Climate (Week 6) - Post 1

Future Climate - Notes

6.1 Notes

In this section, we’ll look at two main approaches to generating future scenarios: those from the Special Report on Emissions Scenarios, and the newer Representative Concentration Pathways approach. Both are attempts to define a range of possible scenarios for the future, which are then used in climate models, and the output from the climate models yields information that helps us think about our future choices.

Learning Goals:

-Explain how emissions scenarios are created and used to drive climate models.

-Describe the families of scenarios defined by the Special Report on Emissions Scenarios.

-Explain what Representative Concentration Pathways represent.

Video Notes

-To model into the future, climate models need to have information about possible emissions scenarios.

-The SRES scenarios start by defining a story of human choices, then figure out a likely emissions pathway for the climate models.

-The RCPs start by defining endpoints for radiative forcing at a future time, then defining representative emissions pathways to get to those endpoints.

-These scenario examples give us information about what the future might hold depending on our choices.

Representative Concentration Pathways (RCPs) Notes:

RCPs are used to project different future pathways for emission scenarios. These projections start with endpoints for radiative forcing in the future, then they work backwards and define the emission pathways that get us to those endpoints. Below is the latest map of projections done by the IIASA, International Institute for Applied Systems Analysis, commissioned from the IPCC for their 5^th assessment report.

As mentioned in the video notes, SRES’s are also used to project future climate scenarios, however they work in the opposite way of RCP’s. SRES’s start with different routes of human behavior, then use climate models to decide the likely emission pathways and endpoints. (SRES projection image is attached below)

-As RCPs have more opportunity for higher accuracy and specification, they have mostly eclipsed SRES’s in official climate reports. 

  

RCP Database: The RCPs, which replace and extend the scenarios used in earlier IPCC assessments, are compatible with the full range of stabilization, mitigation, and baseline emission scenarios available in the current scientific literature.

How the RCP Database Works: The database, which was first released in May 2009, includes harmonized and consolidated data for the four RCPs, comprising emissions pathways starting from an identical base year (2000) to 2100. The database covers emissions of well-mixed greenhouse gases (GHGs) such as carbon dioxide, nitrous oxide and fluorinated gases at the level of five world regions and short-lived GHGs as well as radiatively and chemically active gases (black and organic carbon, methane, sulfur, nitrogen oxides, volatile organic compounds, carbon monoxide and ammonia) in addition to spatial patterns.

Background:

-Radiative forcing is a measure of the influence a factor has in altering the balance of incoming and outgoing energy in the Earth-Atmosphere system and is an index of the importance of this factor as a potential climate change mechanism," according to the IPCC. It is expressed in watts per square meter (W/m²).

-Variations in the sun's output, polar ice, and natural events like volcanic eruptions influence the Earth’s radiative balance, as do human activities that result in, for example, greenhouse gas emissions, pollution, and deforestation. Changes in the resulting radiative forcing level are measured at the top of the atmosphere and calculated by subtracting the energy radiating out from Earth from the energy flowing in and comparing the result against the IPCC base year of 1750 before the onset of the industrialization, where radiative forcing is assumed to be zero. If the level of radiative forcing varies from zero, then some warming or cooling is occurring. Scientists can directly measure the amount by which the Earth’s energy budget is out of balance and calculate the effects that this could have for a range of human and environmental indicators. The four different RCPs were developed to represent the world at different forcing levels in the future. Radiative forcing leading to 8.5 W/m² in 2100, as studied by IIASA using the MESSAGE model, is the high end of the radiative forcing range being used.

RCP Database link:

 http://tntcat.iiasa.ac.at:8787/RcpDb/dsd?Action=htmlpage&page=compare

Here you can test out the four different radiative forcing projections, in accordance with different regions and forcing factors like emissions.

SRES Projection Image:

6.2 Notes

Learning Goals:

-Use a relationship between cumulative carbon emissions and temperature to estimate a remaining carbon emissions budget for humanity.

-Compare the carbon budget to the representative concentration pathways for emissions.

-Describe the role of human choices in determining what will happen in the upcoming century.

-Compare possibilities for future climate over the upcoming tens of thousands of years, depending on the eventual cumulative human carbon emissions.

The human emission budget:

If we go along the worldwide agreement that an increase in overall temperature by 2 degrees is a boundary. For every 1100 total gigatons of carbon emitted the global temperature will increase by 2 degrees, that gives humans a energy budget of 1100 gigatons of carbon. Since the beginning of the 1900s we’ve emitted 540 gigatons of carbon, that means that we have 560 gigatons of carbon left to emit, before we raise the global temperature more then 2 degrees.

Video Notes:

-Every 100 Gigatons of carbon emitted yields about 1.8 C of temperature change (Rise)

-We’ve already emitted about 540 C Gigatons, which leaves about 560 Gigatons in our budget if Earth is going to stay below the 2 C mark.

-The RCP3PD pathway is the only one of the four that keeps global temperatures below 2 C above preindustrial values.

-The greatest source of uncertainty about the future is uncertainty about future human actions.

Reading:

(I did not copy and paste the entire article, I have put in small pieces that outline the information in the article. The article is much longer.)

https://www.nature.com/scitable/knowledge/library/what-happens-after-global-warming-25887608

-As science-journalist Mason Inman (2005) puts it, with only slight exaggeration, "carbon is forever."…Specialists are now investigating the long-term future of our greenhouse gas pollution with the help of a new generation of sophisticated climate models with names like CLIMBER, GENIE, and LOVECLIM. But the basics of that future boil down to one simple principle: what goes up must come down.

Climate Whiplash: Greenhouse gas concentrations and global temperatures will not increase indefinitely — today's carbon dioxide buildup and warming trend must eventually top out and then reverse as the atmosphere gradually recovers. The first stage of this process will occur when the rate at which we burn coal, oil, and natural gas levels off and then declines, either because we switch to alternative energy sources soon, or because we run out of affordable fossil fuels later. As a result, CO₂ concentrations in the atmosphere will also eventually peak and then decline. This, in turn, will cause a series of linked environmental responses in which other currently rising trends reverse one by one in a "climate whiplash" phase that follows the lead of our carbon emissions

After a delay due to slow response times in the atmosphere and oceans (Wigley 2005), global average temperatures will pivot into cooling mode as CO₂ concentrations continue to fall. However, global mean sea level will still rise long after the thermal peak passes, because even though temperatures will be falling, they will still be warmer than today. Therefore, land-based glacial ice will continue to melt and the oceans will continue to expand even though Earth's atmosphere has begun to recover. Sea level will only return to today's position when it finally becomes cool enough for large, land-based ice sheets to build up again on Antarctica and in the Arctic.

Where Does the Carbon Go?: In order to work out the timing of these processes in more detail, one must consider where CO₂ goes after it leaves our smokestacks and exhaust pipes. Some of it will be taken up by soils and organisms but most of it will dissolve into the oceans, with between two thirds and half of our emissions perhaps going into solution during the next millennium or so (Inman 2008, Eby et al. 2009). In many computer simulations, maximum ocean acidification lasts 2000 years or more, depending on the amount of CO₂ we emit in the near future.

The next stage of the cleanup will proceed more slowly. As atmospheric CO₂ dissolves into raindrops, the carbonic acid that it produces will react with calcite and other carbonate minerals in rocks and sediments. Over thousands of years, those geochemical weathering processes will transfer many of the formerly airborne carbon atoms into groundwater and runoff, finally delivering them to the oceans in the form of dissolved bicarbonate and carbonate ions…This slow addition of acid-buffering substances to marine ecosystems will act much like an antacid pill that allows the seas to consume more CO₂ from the overlying atmosphere. These processes are generally expected to dominate the long-term recovery for 5,000 years or so.

But even this second, lengthier phase won't remove the very last fraction of our carbon pollution. Only tens of thousands of years later, or possibly even hundreds of thousands if we burn most of our enormous coal reserves, the last remnants of our CO₂ will finally be scrubbed away by even slower reactions with resistant silicate minerals, such as the feldspars found in granite and basalt.

Choices Before Us:

Choice 1- Moderate Emission Choice-

If we switch to carbon-free energy sources during the next several decades, then approximately 1000 gigatons of fossil carbon will have been released into the atmosphere since the start of the Industrial Revolution (1 gigaton = 1 billion tons). Atmospheric CO₂ concentrations will peak close to 550–600 parts per million (ppm) by 2200 AD or so, and then begin to fall

In the climate whiplash phase that follows this relatively moderate scenario, global mean temperatures are likely to climb 2–3°C higher than today by 2200–2300 AD, then enter a cooling recovery phase lasting as much as 100,000 years. Much of Greenland and western Antarctica's ice will melt into the oceans over millennia, lifting sea levels several meters higher than today before slowly receding.

Choice 2- Business as Usual Emission Choice-

On the other hand, if we burn through all remaining coal reserves before switching to alternative energy sources, then a far more extreme scenario will result. In one computer simulation of what could follow a 5000 gigaton emission, airborne CO₂ concentrations reach 1900–2000 ppm, roughly five times greater than today, by 2300 AD.

Global mean temperature jumps 6–9 °C above today's average and remains artificially high for much longer than it does in the more moderate scenario, with the warmest part of the broad maximum lasting from 3000 AD to 4000 AD. Atmospheric CO₂ concentrations and temperatures then fall relatively steeply for several thousand years after the peak and whiplash phase, but they don't return to today's levels for at least 400,000 years. All land-based ice eventually melts, raising sea levels by as much as 70 meters until the world cools enough for large polar ice sheets to form again, roughly half a million years from now.

Life in a Hothouse:

What might life on Earth be like under such conditions? Although no examples from the past perfectly illustrate the warmest phases of these two scenarios, several of them are nonetheless informative.

Although it was caused by cyclic changes in the orientation of the Earth relative to the sun rather than greenhouse gases, the Eemian example nonetheless shows that even a relatively moderate warming can melt enough land-based ice to raise sea levels by 6–9 meters if it persists long enough, which in this case was 13,000 years.

Fossil oysters resting several meters above the surf zone near Durban, South Africa.

Their elevation shows how high sea level once stood during the warm Eemian Interglacial, 130,000–117,000 years ago.

 

Fossil oysters resting several meters above the surf zone near Durban, South Africa. Their elevation shows how high sea level once stood during the warm Eemian Interglacial, 130,000–117,000 years ago

 

Geo-historical evidence shows that the Paleocene-Eocene Thermal Maximum (PETM) was triggered by greenhouse gas buildups, most likely from the release of icy methane hydrates or other carbon compounds buried in marine deposits. Global mean temperatures rose 5–6°C within several thousand years and did not fully recover for 100,000–200,000 years. Both polar regions were completely ice-free, the Arctic Ocean was a warm, brackish pond rimmed by deciduous redwood forests, Antarctica was covered by beech trees, and carbonic acid burned a discolored, carbonate-free band into ocean sediments worldwide. Some species became extinct during the PETM, especially in the most heavily acid-impacted portions of the oceans

*In both of these cases, free migration seems to have been an important key to the survival of animals and plants of the time, and the lack of human-made barriers in the distant past made it easier for species to adjust to large climatic shifts. Unfortunately, our settlements, roads, and farms can make such migrations more difficult today, and will probably do so in the future as well.*

Climate Ethics:

Our carbon emissions will influence countless generations, as well as many species other than our own, in future versions of the world that will differ markedly from the one we know now. This realization may force us to weigh the needs of some generations against those of others.

-For instance, having the Arctic Ocean become ice-free in summer may seem outlandish to us, but it may instead seem normal to people who will be born into a warmer world thousands of years from now. When the global cooling recovery sets in, the open-water ecosystems and human cultures that will by then have become dependent upon warmer climates could be threatened as the polar ocean begins to re-freeze.

-Another potentially confusing situation arises when we consider that atmospheric CO₂ concentrations will still be high enough in 50,000 AD to prevent the next ice age, which natural cyclic processes would normally be expected to trigger then. The next major cyclic cool period is due in 130,000 AD, by which time a moderate carbon emission will have dissipated. This suggests that preventing an extreme 5000 Gton hothouse scenario now could leave Canada and northern Europe vulnerable to being bulldozed by gigantic ice sheets in the deep future.

Conclusion:

Fortunately, long-term perspectives may also suggest possible win-win situations, as well. For instance, leaving most remaining coal untouched rather than using it all up now would reduce the severity of climate change in the near-term, and would also leave large stores of burnable carbon in the ground that later generations could use as a source of greenhouse gases for the prevention of future ice ages, should they so desire.

Whichever emissions scenario we choose-be it moderate or extreme-one thing is now clear. Our influence on the climatic future of the world is geological in scope. Little wonder, then, that many scientists are now referring to our chapter of Earth history with a term coined by ecologist Eugene Stoermer-the "Anthropocene Epoch" or the "Age of Humans"

6.3 Notes

Learning Goals:

-Compare your own mental model of the climate system today to your mental model of the climate system a few weeks ago.

-Describe possible future climate changes, involving some particular aspect of the climate system, of interest to you (if there are any quiz questions on this one they would be from the Arctic reading).

Reading:

https://www.pmel.noaa.gov/arctic-zone/future/bib/EarthsFutureJEO.pdf

Future Arctic climate changes: Adaptation and mitigation time scales

Abstract:

The climate in the Arctic is changing faster than in midlatitudes. This is shown by increased

temperatures, loss of summer sea ice, earlier snow melt, impacts on ecosystems, and increased economic

access. Arctic sea ice volume has decreased by 75% since the 1980s. Long-lasting global anthropogenic

forcing from carbon dioxide has increased over the previous decades and is anticipated to increase

over the next decades. Temperature increases in response to greenhouse gases are amplified in the

Arctic through feedback processes associated with shifts in albedo, ocean and land heat storage, and

near-surface longwave radiation fluxes. Thus, for the next few decades out to 2040, continuing environmental changes in the Arctic are very likely, and the appropriate response is to plan for adaptation

to these changes. For example, it is very likely that the Arctic Ocean will become seasonally nearly sea

ice free before 2050 and possibly within a decade or two, which in turn will further increase Arctic temperatures, economic access, and ecological shifts. Mitigation becomes an important option to reduce

potential Arctic impacts in the second half of the 21st century. Using the most recent set of climate model

projections (CMIP5), multimodel mean temperature projections show an Arctic-wide end of century

increase of +13 C in late fall and +5 C in late spring for a business-as-usual emission scenario (RCP8.5) in

contrast to +7 C in late fall and +3 C in late spring if civilization follows a mitigation scenario (RCP4.5).

Such temperature increases demonstrate the heightened sensitivity of the Arctic to greenhouse gas

Key Points:

-Loss of sea ice over the next three decades will amplify Arctic climate change.

-Carbon mitigation can slow down changes to late-century Arctic temperatures.