When could global warming reach 4°C? (original) (raw)
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Global Warming in the 21st Century: An Alternate Scenario
2000
A common view is that the current global warming rate will continue or accelerate. But we argue that rapid warming in recent decades has been driven by non-CO2 greenhouse gases (GHGs), such as CFCs, CH4 and N20, not by the products of fossil fuel burning, CO2 and aerosols, whose positive and negative climate forcings are partially offsetting. The growth rate of non-CO2 GHGs has declined in the past decade. If sources of CH4 and 03 precursors were reduced in the future, the change of climate forcing by non-CO2 GHGs in the next 50 years could be near zero. Combined with a reduction of black carbon emissions and
Global Warming: some back-of-the-envelope calculations
We do several simple calculations and measurements in an effort to gain understanding of global warming and the carbon cycle. Some conclusions are interesting: (i) There has been global warming since the end of the "little ice age" around 1700. There is no statistically significant evidence of acceleration of global warming since 1940. (ii) The increase of CO_2 in the atmosphere, beginning around 1940, accurately tracks the burning of fossil fuels. Burning all of the remaining economically viable reserves of oil, gas and coal over the next 150 years or so will approximately double the pre-industrial atmospheric concentration of CO_2. The corresponding increase in the average temperature, due to the greenhouse effect, is quite uncertain: between 1.3 and 4.8K. This increase of temperature is (partially?) offset by the increase of aerosols and deforestation. (iii) Ice core samples indicate that the pre-historic CO_2 concentration and temperature are well correlated. We conclu...
Climatic Change, 2011
A wide variety of scenarios for future development have played significant roles in climate policy discussions. This paper presents projections of greenhouse gas (GHG) concentrations, sea level rise due to thermal expansion and glacial melt, oceanic acidity, and global mean temperature increases computed with the MIT Integrated Global Systems Model (IGSM) using scenarios for twenty-first century emissions developed by three different groups: intergovernmental (represented by the Intergovernmental Panel on Climate Change), government (represented by the U.S. government Climate Change Science Program) and industry (represented by Royal Dutch Shell plc). In all these scenarios the climate system undergoes substantial changes. By 2100, the CO 2 concentration ranges from 470 to 1020 ppm compared to a 2000 level of 365 ppm, the CO 2-equivalent concentration of all greenhouse gases ranges from 550 to 1780 ppm in comparison to a 2000 level of 415 ppm, oceanic acidity changes from a current pH of around 8 to a range from 7.63 to 7.91, in comparison to a pH change from a preindustrial level by 0.1 unit. The global mean temperature increases by 1.8 to 7.0 • C relative to 2000. Such increases will require considerable adaptation of many human systems and will leave some aspects of the earth's environment irreversibly changed. Thus, the remarkable aspect of these different approaches to scenario development is not the differences in detail and philosophy but rather the similar picture they paint of a world at risk from climate change even if there is substantial effort to reduce emissions.
HISTORICAL AND PREDICTED GLOBAL CLIMATE CHANGES AND CLIMATE MITIGATION APPROACHES
San Francisco Global Climate Action Summit, 2018
This presentation summarizes the results of global climate models which have been developed and employed to predict annual increases in greenhouse gases and their effect on average global temperature increases from year-end 2016 to year-end 2031. These models predict that average global temperatures could reach 1.50 degrees C (+2.72 degrees F) by year-end 2025 and 2.09 degrees C (+3.76 degrees F) by year-end 2031 compared to the average global temperatures at year-end 1970. Therefore, the initiation of a global climate “tipping point” has a reasonable probability of occurring before 2031. The predicted atmospheric increases in water vapor and reductions in surface albedo, due to increasing global temperatures, are projected to significantly modify global weather patterns and escalate extreme precipitation in some areas concurrent with drought periods in other regions. The expected increases of greenhouse gases and global temperatures originally predicted from the 2016 model are compared with published data at the end of 2021. To date, this model has accurately predicted the average temperature increases and increased atmospheric concentrations of CO2, N2O, CH4, and H2O, as well as Albedo (Earth’s surface reflectivity) from year-end 2016 to 2021. Although the average global temperature has increased by 1.23 degrees C (2.22 degrees F) from 1970-2021, many areas have experienced a much greater temperature increase. For example, the average temperature increases from 1970-2021 during the summer in California has been 3.5 degrees C (6.3 degrees F). Several mitigation approaches are described that may help delay the timing for this impending potential “tipping point.” Recommended approaches include the efficient and economical conversion of CO2 emissions and CO2 captured from ambient air; CH4 emissions from oil wells; and waste biomass into low-carbon fuels and hydrocarbon feedstocks for plastic production. This presentation was originally developed in support of the Under2Coalition, which was established between California and Germany’s state of Baden-Württemberg in 2015, and which currently encompasses members from more than a third of the world’s economies.
Greenhouse-gas emission targets for limiting global warming to 2 °C
Nature, 2009
More than 100 countries have adopted a global warming limit of 2 6C or below (relative to pre-industrial levels) as a guiding principle for mitigation efforts to reduce climate change risks, impacts and damages 1,2 . However, the greenhouse gas (GHG) emissions corresponding to a specified maximum warming are poorly known owing to uncertainties in the carbon cycle and the climate response. Here we provide a comprehensive probabilistic analysis aimed at quantifying GHG emission budgets for the 2000-50 period that would limit warming throughout the twenty-first century to below 2 6C, based on a combination of published distributions of climate system properties and observational constraints. We show that, for the chosen class of emission scenarios, both cumulative emissions up to 2050 and emission levels in 2050 are robust indicators of the probability that twenty-first century warming will not exceed 2 6C relative to pre-industrial temperatures. Limiting cumulative CO 2 emissions over 2000-50 to 1,000 Gt CO 2 yields a 25% probability of warming exceeding 2 6C-and a limit of 1,440 Gt CO 2 yields a 50% probability-given a representative estimate of the distribution of climate system properties. As known 2000-06 CO 2 emissions 3 were 234 Gt CO 2 , less than half the proven economically recoverable oil, gas and coal reserves 4-6 can still be emitted up to 2050 to achieve such a goal. Recent G8 Communiqués 7 envisage halved global GHG emissions by 2050, for which we estimate a 12-45% probability of exceeding 2 6C-assuming 1990 as emission base year and a range of published climate sensitivity distributions. Emissions levels in 2020 are a less robust indicator, but for the scenarios considered, the probability of exceeding 2 6C rises to 53-87% if global GHG emissions are still more than 25% above 2000 levels in 2020.
Assessing the 2018 U.N. IPCC Special Report, Global Warming of 1.5 °C
Kamada Science & Design, 2019
The latest IPCC (U.N. Intergovernmental Panel on Climate Change) Special Report, authored by 91 scientists from 40 nations, says we have already warmed the planet by roughly 1.0 degrees Celsius (°C) (1.8 °F). (1) And, if business remains as usual, we have only 12 years left before we have locked in an additional 0.5 °C (0.9 °F), for a total of 1.5 °C of global warming, since the 20th century began. However, Michael Mann and other prominent climate scientists say, as with previous IPCC reports, that this estimate is again watered-down and overly optimistic. Mann also suggests that global warming since 1900 has been slightly greater than the IPCC report claims. (2) They place the blame on the IPCC’s requirement for near-unanimity among, not just the authors, but also their reviewers (which may include bureaucrats and politicians), prior to formal publication. The often more dire, most recent, scientific literature results also tend to be discounted for the same reasons. Though their criticisms maybe be valid, that alone does not provide a quantitative basis for assessing the latest IPCC findings. Here, to address these concerns we present three quantitative estimates based on three different methods, all suggesting that the IPCC report presents, more than a best-case scenario, rather an incredibly optimistic one. Assuming “business as usual”, the approaches outlined below yield a tight cluster of estimates of 14.8, 14.8, and 12.8 years remaining to lock in, not just 1.5 °C but rather 2.0 °C of warming since 1900. Thus, even the high-end estimate of 14.8 years suggests that the IPCC’s forecast of 1.5 °C at the 12 year mark seems overly optimistic by more than 0.4 °C.