Paris-Beacon-Of-Hope
 

 

 Home     Summary     Resources     FAQ     More Info

 

Paris Climate Agreement: Beacon of Hope

Summary

Messages of our book include:

1) variations in global temperature are driven by fluctuations in atmospheric CO2 and other greenhouse gases (GHGs) on both geologic and recent time scales

2) global warming over the past 150 years is clearly due to the human-induced rise in CO2

3) the climate models used by IPCC (2013) warm too quickly compared to actual data and, therefore, society has a better chance of averting climate catastrophe than is commonly appreciated

4) the pledges upon which the Paris Climate Agreement is based place the world on the right track to achieve the GHG emission reductions needed to achieve either the Paris target (1.5C rise in temperature) or upper limit (2C rise), provided:

  • unconditional and conditional pledges are followed

  • reduction in GHG emissions needed to achieve the Paris Climate Agreement are extended out to year 2060

Finally and most importantly:

5) limiting global warming to 2C will require half of all global energy to be produced by either renewables in year 2060 or by combustion of fossil fuel coupled to efficient carbon capture and sequestration ... we repeat, half of all global energy. This will require a massive transformation in how energy is produced, both in the developed and developing world. The time to start is now!

Here are a few figures that support these conclusions:

Message #1: variations in global temperature are driven by fluctuations in atmospheric CO2 and other greenhouse gases (GHGs) on both geologic and recent time scales

The black line shows the historical evolution of the global mean surface temperature anomaly with respect to a pre-industrial baseline (i.e., change in temperature throughout Earth's history relative to the temperature that occurred during 1850 to 1900) and the blue line shows estimates of the atmospheric abundance of carbon dioxide (CO2).  Major events in the evolution of life on Earth as well as either climate or the global carbon cycle are also noted.  Finally, horizontal lines denote 280 ppm (pre-industrial CO2), 400 ppm (atmospheric CO2 at time of book publication), and 560 ppm (twice pre-industrial CO2). After Figure 1.1

The scientific message of this figure is that over our planet's history, Earth has warmed and cooled in a manner closely associated with increases and decreases of atmospheric CO2

Message #2: global warming over the past 150 years is clearly due to the human-induced rise

in CO2

The black line shows the rise in global mean surface temperature, from 1850 to present, based on measurements provided by the Climate Research Unit (CRU) of the University of East Anglia, United Kingdom.  The red line shows the best estimate of radiative forcing of climate due to all human activities, provided by the Intergovernmental Panel on Climate Change (IPCC) and maintained at the Potsdam Institute for Climate Research. After Figure 1.3

The scientific messages of this figure are:

a) global mean surface temperature has warmed by about 0.83 C in response to an increase in the radiative forcing of climate of about 2.1 watts per square meter during past century and a half

b) the rise in global mean surface temperature closely follows the shape of radiative forcing due to rising GHGs, the most important of which happens to be CO2

Section 1.2.3 of the book, entitled Human Fingerprints, includes extensive discussion and illustration of the quantitative consistency between various aspects of observed and expected changes in atmospheric temperature and composition, which allow us to confidently conclude human activity is responsible for the rise in temperature over the past 165 years shown above.

EM-GC: The book uses analysis and projections of global mean surface temperature conducted using a computational tool called the Empirical Model of Global Climate (EM-GC).  Our model is described in this journal article Canty et al., ACP, 2013. Simply put, as shown below, we calculate the influence on global mean surface temperature of human activity, major volcanoes, variations in solar irradiance, as well as exchange of heat between the ocean and atmosphere due to a phenomena known as the El Nio Southern Oscillation (ENSO), changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC), the Pacific Decadal Oscillation (PDO), and the Indian Ocean Dipole (IOD).  The long-term transport of heat from the atmosphere to the ocean is explicitly represented based on simulation of the observed rise in ocean heat content (OHC).

This figure shows the measured (top panel, black)  and simulated (red) global mean surface temperature anomaly (ΔT), contributions to the simulated rise in ΔT from humans and various other factors (middle panels), as well as observed and modeled ocean heat content (bottom panel). This particular simulation used the RCP 4.5 scenario for radiative forcing (RF) due to GHGs and aerosols, tied to IPCC (2013) best estimate of RF due to aerosols in year 2011 of -0.9 W m-2. After Figures 2.05, 2.09, and 2.10

We then project future warming based on values of climate feedback (parameter λ) and eddy heat diffusion coefficient (parameter κ) inferred from the actual temperature record, assuming neutral conditions for future ENSO, Volcanoes, Solar, AMOC, etc and continuation of the rise in OHC. As  explained in Chapter 2, these projections consider a wide range of uncertainties regarding radiative forcing of climate due to GHGs and a class of human pollution called aerosols, as well as various data records for ocean heat content.

Message #3a: climate models used by IPCC (2013) warm too quickly:

 

The colored symbols show estimates of AAWR, the Attributable Anthropogenic Warming Rate, inferred from the climate record for 1979 to 2010 using the Empirical Model of Global Climate (EM-GC) analysis of data for global temperature from the Climate Research Unit (CRU) of East Anglia, UK.  Error bars on each point show the uncertainty in AAWR due to imprecise knowledge of how tropospheric aerosols (suspended particles, generally from human activity) affect climate. The various colors within each group represent use of a different dataset for rise in OHC over this 32 year period of time. The right-most  symbol depicts AAWR inferred from the Climate Model Intercomparison Project #5 (CMIP5) archive of Global Climate Model (GCM) simulations. This symbol, a box and whisker plot, shows the median (middle line), 25th and 75th percentile (lower and upper edges of the box), and minimum & maximum (vertical extent of lines) of AAWR from 41 GCMs.  After Figure 2.13

The scientific message of the figure is that human activity has caused the actual climate system to warm by about 0.11C per decade from 1979 to 2010, whereas climate models project a warming of about 0.22C per decade should have occurred. Section 2.3 of the book compares and contrasts these estimates of AAWR to other values in the scientific literature.

The CMIP5 models used by IPCC (2013) suggest that RCP 2.6, which poses stricter controls on the emission of GHGs, is the 2C pathway.

Message #3b: society has a better chance of averting climate catastrophe than is commonly appreciated:

These figures show probability distribution functions (PDFs) of the rise in global mean surface temperature that will occur in years 2060 (top) and 2100 (bottom), relative to a pre-industrial baseline, based on our Empirical Model of Global Climate (EM-GC) forecasts (blue) and from CMIP5 GCMs (red). By definition, the total area under each curve is unity. Every horizontal line segment shows the probability (height) that the future rise in temperature will be confined to a value between two values (edges of the segment). The target (1.5C warming) and upper limit (2C warming) goals of the Paris Climate Agreement are also shown. The left panels show projections of global warming calculated if the atmospheric GHGs follow the so-called RCP 4.5 trajectory; the right panels are for RCP 8.5. The uncertainty in the EM-GC forecast of global warming, for any specific RCP scenario, is dominated by imprecise knowledge of how tropospheric aerosols and clouds affect climate. After Figures 2.17 and 2.18

The scientific message of the PDF figures is that if GHG emissions can be limited to those of RCP 4.5 then by end-century there is:

a) a 75% probability the Paris target of 1.5C warming above pre-industrial will be achieved

b) a greater than 95% probability the Paris upper limit of 2C warming will be achieved

In other words, our analysis suggests RCP 4.5 is the 2C pathway !

The CMIP5 models used by IPCC (2013) suggest that RCP 2.6, which poses stricter controls on the emission of GHGs, is the 2C pathway.

The figure above, included for those not familiar with the climate modeling world, shows time series of the three most important anthropogenic GHGs: carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), from the RCP 8.5, 4.5, and 2.6 scenarios. RCP stands for Representative Concentration Pathway and the number of each scenario denotes the increased in radiative forcing of climate, units watts per square meter, that will result by end of century. After Figure 2.1

Again, simulations conducted using our Empirical Model of Global Climate indicate that if the future emissions of GHGs can be reduced such that atmospheric abundances follow the RCP 4.5 trajectory, there is a high probability the goal of the Paris Climate Agreement will be achieved. In other words, carbon emissions must be reduced such that the future atmospheric abundance of CO2 remains below about 540 ppm (parts per million) and the future growth of atmospheric CH4 must be halted. In Section 4.4.2 of the book, we quantify how the future growth of atmospheric CH4 impacts the probability of achieving the goal of the Paris Climate Agreement, should atmospheric CO2 follow RCP 4.5 and should CH4 continue to rise.

Message 4: the Paris INDCs* place the world on the right track to achieve the GHG emission reductions needed to achieve the goals of the Paris Climate Agreement, provided:

  • unconditional and conditional pledges are followed

  • reductions in GHG emissions extend out to year 2060

The figure above shows global emissions of the three most important anthropogenic GHGs, CO2 CH4 and N2O, expressed in a metric called CO2-equivalent (CO2-eq) that is used in the climate policy community.  The colored lines show emissions for the RCP 2.6, 4.5, and 8.5 scenarios; the dark grey line shows CO2-eq emissions projected for either Business as Usual (BAU) (i.e., emissions driven by economic forces) (left), adherence to only the Paris Unconditional INDCs out to the specified end year which is typically 2030 followed by BAU (middle), and adherence to all of the Unconditional and Conditional Paris INDCs  followed by continued reductions in GHG emissions (right).  Finally, the shaded grey region reflects our estimate of the uncertainty in future GHG emissions due to population. After Figures 3.8a, 3.9a, and 3.11a

The scientific message of this figure is that, if all of the Paris INDCs are followed and if the world continues to reduce GHG emissions out to year 2060 in a manner that builds on the reductions needed to achieve the Paris INDCs, then global emissions of GHGs could be quite similar to those used to drive RCP 4.5.

*During the COP 22 meeting held in Marrekech, Morocco, the INDCs became known as NDCs since the Paris Climate Agreement was "in effect".  Here and throughout we use INDCs since "Intended" was part of the working definition during summer 2016, when the content of our book was finalized.

Message 5: limiting global warming to 2C will require half of all global energy to be produced by either renewables in year 2060 or by combustion of fossil fuel coupled to efficient carbon capture and sequestration.

This figure shows a projection of world energy needs provided by the US Energy Information Administration (EIA) and the means upon which these energy needs will be met for either a business as usual approach (emissions driven by economic forces) (left), the growth in energy production by renewable sources and the decline in energy production by combustion of fossil fuel needed to place global emissions of GHGs on RCP 4.5 staring in year 2030 (middle), and the growth in energy production by renewables, the rise of carbon capture and sequestration (CCS) coupled to fossil fuel sources, and the decline in energy production by combustion of fossil fuels not coupled to CCS needed to place global emissions of GHGs on RCP 2.6 staring in year 2030 (right).  After Figures 4.02a, 4.03a, and 4.05a

The message of this figure is that to keep GHG emissions below that of RCP 4.5 in year 2060, and at the same time meet a projection of future global energy needs, the world must produce a considerable portion of global energy using sources that do not emit GHGs, with this portion rising to about 50% by year 2060.  To achieve the steeper GHG emission reductions of RCP 2.6, the key metric is about 90% of total global energy without releasing GHGs by year 2060.

For more information, explore this website and

either download or purchase a copy of the book.

 

Finally, please email us at parisbeaconofhope@gmail.com
if any of the URLs are not working, if anything else seems amiss
with this webpage, or if you'd like to correspond with us
regarding the content of the book.
We can also be reached at our regular work email addresses.
 
 

This page last updated on Monday, 31 July 2017