What will it take to limit climate change to 1.5 degrees C?

The 1.5°C marker pathway is the most challenging mitigation pathway that can still be defended as being techno-economically achievable.  It is endorsed by the Pope and many religious leaders. The last IPCC report said feasible scenarios for bringing temperatures down below 1.5C are “characterized by (1) immediate mitigation action; (2) the rapid upscaling of the full portfolio of mitigation technologies; and (3) development along a low‐energy demand trajectory.”[1]  The costs of this action are modest, even before taking into account health improvements and energy-security benefits. Delay reduces options and increases costs.[2]

A 1.5°C cap reduces the remaining carbon budget for the 21st century to almost half that of the 2°C path;  carbon neutrality must be achieved 10-20 years earlier than the 2°C track, and faster improvements in energy efficiency are required.[3] Figuring global emissions reduction rates from 2013, Baer et al. estimated that reasonable likelihood of achieving it would require average reducing emissions by 9% for CO2 and 7.1% for all gases (whereas a 66% chance of hitting 2°C would require reductions each year of less than half of that, for all gases, 3.4%). They also showed that only the 1.5°C path can make it likely that we will achieve 2C.

Steepness of reductions with IPCC paths

Steep reductions in emissions now are necessary on even the 2 C path

Steepness of emission reductions

Reductions in GHGs must be faster, nearly impossibly so, the longer we wait

A rapid shift is possible, but we must begin now. The later we start the steeper and faster the transition will have to be completed.   Further, we run the risk of irreparably damaging the ocean, the longer we continue on the current path even if the CO2 emitted could somehow be absorbed in the future.[4]

  • Immediate cuts in greenhouse gas emissions, scaling up quickly over the next decade. The 1.5°C goal leaves no space to delay action on decarbon-isation.  Religious leaders echo the call; The Pope has said we must transition off fossil fuels “without delay” (LS 165).
    • New investment in and construction of carbon emitting power plants should stop, due to health effects and the emissions they lock in.
    • Transition existing infrastructure off the most-polluting fossil fuels in the next 10-20 yrs.
  • The air can no longer be a place for free dumping/pollution. Dumping in the atmosphere ruins our common home and the cycles and life support systems on which life depends. It costs lives.
  • Major players and biggest emitters will need to make bigger more ambitious commitments and stick to them. The world is not on track to stave off the worst effects of climate change.  The present analysis of intended nationally determined contributions (so called INDCs) funded by the European Commission and conducted by leading research teams from Brazil, China, Japan, India, the US and the EU (Potsdam Institute) of national GHG emission reduction plans found they leave too much inefficient and unabated fossil fuel capacity online in 2030 to be coherent even with a 2°C scenari This highlights the risks of lock-in into a high carbon trajectory with fossil-based investments if action is not strengthened quickly.
  • Deeper cuts are needed by all sooner rather than later (next 5-6 years) especially in energy and industry.Carbon countdown
  • Renewable energy needs to be a much bigger part of the picture, sooner rather than later and oil, gas, and especially coal will need to be kept in the ground this century. For example 88% of coal, globally, will need to be kept in the ground, plus 52% of gas and 35% of oil.[5]
  • Carbon emissions will need to become negative at a global scale this century, with significant restoration of forests, savannahs, grasslands. Keeping (mitigating) climate change to 1.5°C will ease pressure on food supply systems but challenges will remain from the warming already built in, which will be encountered for at least 30 years after GHG emissions cease or become negative, at a global scale. Costa Rica became the first country to pledge carbon neutrality by 2021 last year. Even with this action, “Basically all our 1.5°C scenarios first exceed the 1.5°C temperature threshold somewhere in mid-century,” but it is still possible to stabilize at 1.5°C this century with prompt action.

Stanford University research (Jacobson et al.) developed all-sector energy roadmaps for 139 countries of the world, based on 100% clean and renewable wind, water, and sunlight (WWS),[6] demonstrating that the transition is not only possible, it would virtually eliminating air pollution morbidity and mortality and global warming.  Implementation of these roadmaps will create net jobs worldwide, stabilize energy prices because fuel costs are zero, reduce international conflict over energy because each country will largely be energy independent, and reduce terrorism risk by significantly decentralizing power.

This transition will save 27.9% of the energy needed due to the greater efficiency of electricity over combustion.  Over the 139 countries, converting will create an estimated 22.8 million 35-year construction jobs and 17.5 million 35-year operation jobs for the energy facilities alone, the total outweighing the 37.3 million jobs lost by around 3 million.  Of importance in considering life, health, and well-being, not to mention worker productivity, converting to WWS will eliminate in the range of 4.6 (1.3-8.0) million premature air pollution mortalities per year. Further, around $3.2 ($0.9-$5.9) trillion/year in health costs (2013 dollars), would be saved, equivalent to 4.38 (1.25-8.03) percent of the 2012 139-country gross domestic product.  It will further eliminate about $16 (9-34) trillion/year in 2050 global warming costs (2013 dollars) due to 139-country emissions.  Individuals worldwide will see substantial savings in fuel costs, health costs (an order of magnitude higher), and climate costs even five times higher than that.

Personal carbon budgets in developed countries will also need to decline, as illustrated in the example to the right.Personal carbon budget


International Institute for Applied Systems Analysis, http://www.iiasa.ac.at/web/home/about/news/150521-15-scenarios.html .  Summary Report of the Structure Expert Dialogue, Lima, Peru, 2–3 December 2014, Geneva, Switz, 8–9 Feb  2015.  http://www.climateemergencyinstitute.com/uploads/Summ_report_Expert_UNFCCC_1.pdf.

Hare, B., Schaeffer M, Serdeczny O. & Friedrich-Schleussner C (2014). “Can global warming be limited to 1.5C?” http://www.rtcc.org/2014/11/24/can-global-warming-be-limited-to-1-5c/#sthash.oGGQVwlw.dpuf

Jacobson, et al., Sector by Sector Wind, Water, and Solar Power Analyses and Transition Plans for 139 Countries.” Aug. 2015. See summary paper, xlsx-spreadsheets, % of 2050 WWS installed as of 2014, Wind installed as of 2014, PV installed as of 2014, CSP installed as of 2014,Hydro installed as of 2014, Geothermal installed as of 2014, Tidal installed as of 2014. Sectors and infrastructure addressed include electricity, transportation, heating/cooling, industry, and agriculture/forestry/fishing.

Luderer G, Bertram C, Calvin K, et al. (2013) Implications of weak near-term climate policies on long-term mitigation pathways. Clim. Change online fir:

Rogelj J, McCollum DL, O’Neill BC, Riahi K (2013a) 2020 emissions levels required to limit warming to below 2 °C. Nat Clim Chang 3:405–412. doi: 10.1038/nclimate1758

Rogelj J, McCollum DL, Reisinger A, et al. (2013b) Probabilistic cost estimates for climate change mitigation. Nature 493:79–83. doi: 10.1038/nature11787

Rogelj J, Luderer G, Pietzcker RC, Kriegler E, Schaeffer M, Krey V, Riahi K. (2015). Energy system transformations for limiting end-of-century warming to below 1.5°C. Nature Climate Change. 21 May 2015. DOI: 10.1038/NCLIMATE2572http://phys.org/news/2015-05-limit-climate.html

Schaeffer M, Hare W, Rahmstorf S, Vermeer M (2012) Long-term sea-level rise implied by 1.5 °C and 2 °C warming levels. Nat Clim Chang 3–6. doi: 10.1038/nclimate1584

Science Daily, (2015) “Two degree Celsius climate change target ‘utterly inadequate’.” 27 March 2015.

Tschakert, P. (2015) 1.5°C or 2°C: a conduit’s view from the science-policy interface at COP20 in Lima, Peru. Climate Change Responses  2:3 DOI 10.1186/s40665-015-0010-z

UNEP (2014) Emissions gap report. Literature on 1.5C scenarios. Opportunities lost every decade emissions rise.

World Bank (2014), “Turn Down the Heat: Confronting the New Climate Normal”.

[1] IPCC Report (2014), WGIII SPM page 17.

[2] Luderer et al., 2013b; Rogelj et al., 2013a; Rogelj et al., 2013b. When action is delayed, various options to achieve stringent levels of climate protection are increasingly lost

[3] Joeri Rogelj, Gunnar Luderer, Robert C. Pietzcker, Elmar Kriegler, Michiel Schaeffer, Volker Krey, Keywan Riahi. Energy system transformations for limiting end-of-century warming to below 1.5 °CNature Climate Change, 2015; 5 (6): 519 DOI: 10.1038/NCLIMATE2572

[4] The oceans have absorbed 93% of the global warming that has occurred to date.  Researchers have found that even if humanity had a way of removing CO2 from the atmosphere in the future (outside of slow removal by trees and intact grasslands), if emissions continue, warming and CO2 and the associated reduced oxygen, reduced circulation, and acidified water will kill many species. See:https://www.awi.de/nc/en/about-us/service/press/press-release/the-oceans-cant-take-any-more-researchers-fear-a-fundamental-change-in-the-oceans-even-if-gr.html.  “Greenhouse gases’ millennia-long ocean legacy.” ScienceDaily. 3 August 2015. <www.sciencedaily.com/releases/2015/08/150803155059.htm>

[5] See graphic below.  Only a quarter of fossil fuels can be burned and only a small fraction of coal reserves can be burned to keep warming to relatively safe levels.Only can afford to burn a quarter of fossil fuel reserves

[6] Jacobson, MZ et al., 2015. See summary paper, xlsx-spreadsheets, % of 2050 WWS installed as of 2014, Wind installed as of 2014, PV installed as of 2014, CSP installed as of 2014,Hydro installed as of 2014, Geothermal installed as of 2014, Tidal installed as of 2014. Sectors and infrastructure addressed include electricity, transportation, heating/cooling, industry, and agriculture/forestry/fishing.  As of the end of 2014, 5.5% of the WWS energy generation capacity needed for a 100% world has already been installed in these countries, with Paraguay (73.1%), Norway (62.2%), and Tajikistan (50.2%) exceeding 50%. The roadmaps envision 80-85% conversion by 2030 and 100% conversion of all countries by 2050. Transforming may reduce 2050 power demand relative to BAU by ~27.9% due to the efficiency of electricity over combustion and another ~6.9% due to end-use efficiency beyond that already occurring in the BAU case. Remaining annually averaged 2050 demand may be met with a mean of ~23.2% onshore wind, ~15.1% offshore wind, ~28.0% utility-scale photovoltaic (PV), ~8.9% residential rooftop PV, ~8.6% commercial/government/parking rooftop PV, ~6.9% concentrated solar power (CSP), ~1.1% geothermal power, ~0.85% wave power, ~0.07% tidal power, and ~7.2% hydropower. The new plus existing nameplate capacity of generators across all 139 countries is 30.9 TW, which represents only 1.3% of the technically possible installed capacity based on resource analysis. http://web.stanford.edu/group/efmh/jacobson/Articles/I/CountriesWWS.pdf