Table of Contents:
Introduction: What Key Low-Carbon Technologies are Needed to Meet Serious Climate Mitigation Targets and What is their Status?
Since the industrial revolution, humanity has emitted Gigaton quantities of carbon dioxide (CO,) and other greenhouse gases. Figure 1 (NASA GISS, 2019) shows that the warming that has occurred since 1880 has been in the order of 1.1 degrees centigrade higher than pre-industrial levels. As a result of manmade emissions, carbon dioxide concentrations har e dramatically spiked to unprecedented levels when viewed from an 800,000-year perspective. Current concentrations of carbon dioxide are now approximately 410 PPM, relative to the 280-ppm level just before the industrial revolution. Note that in the absence of a serious global emission reduction program. CO, concentrations are projected to rise as high as 1000 ppm later this century.
Figure 2 compares actual wanning (NASA GISS, 2019) to model projections. The model used was the Model for the Assessment of Greenhouse Gas Induced Climate Change (MAGICC), using middle of the road model assumptions and assuming a fossil fuel intensive emission trajectory (A1FI). It is important to note the close correlation of the actual warming relative to the model projections. As can be seen, if we continue on this fossil fuel intensive emission path and the model continues to accurately predict warming, the planet would be 1.5 °C warmer by 2035 and 2 °C wanner by 2045. These warming levels are particularly relevant since the international community has set a wanning target of no greater than 2 °C and optimally below 1.5 °C by the end of this century. If we were to continue on our current fossil fuel intensive trajectory, 2100 warming is projected to be greater than 4 °C and rising.
To put the significance of such warming in perspective, Figure 3 was generated based on data from a reconstruction of global temperature for the last 11,300 years (Marcot, 2013), with more recent warming data and model projections included. When crment and projected warming is viewed from this long-term perspective, it becomes clear that humankind has, in just 240 years, fundamentally changed the heat transfer characteristics of the planet, with even more dramatic change projected. Note that, as of 2017, wanning was about 0.2 °C warmer than any time in the last 11,300 years. If we continue on our fossil fuel intensive emission trajectory, wanning is projected to be in the order of 3.5 °C greater than any time over this period.
Figure 1. Wanning that has declined since industrial revolution.
Figure 2. Actual global warming compared to a model projection.
Only Emissions of Greenhouse Gases (GHGs) Can Account for the Warming Experienced Since the Industrial Revolution
As discussed, it is clear that the planet has wanned considerably since the industrial revolution. A legitimate question Is whether such wanning is a result of human emissions of greenhouse gases or the result of natural factors, such as solar variations and volcanic emptions. Such emptions can cool the planet after the reflective particles are driven into the stratosphere, while the planet could warm back up after the particles have settled out of the atmosphere. Figure 4 (USEPA, 2017) illustrates that when
Figure 3. Temperature change (relative to the 1961-1990 mean) overpast 11,300 years (in blue) plus projected warming this
century on humanity’s current emissions path (in red).
Figure 4. Only GHG emissions can explain warming since 1900.
comparing actual wanning to warming predicted by models when only natural factors are considered versus when one accounts for the greenhouse gas impacts, it is clear that human GHG emissions have provided the driving force for the observed wanning. Note that Figure 2 reinforces this conclusion, since model wanning projections, assuming only GHG emission impacts, yield results consistent with the actual warming.
The Heat Added by Anthropogenic Emissions of GHGs is Already Yielding Major Impacts, with More to Come
It is not possible to change the heat balance of the earth so substantially, as humanity has done by adding large quantities of GHGs, without major impacts. It has been calculated (Skeptical Science, 2019) that
Figure 5. The unpacts of greenhouse gas emissions.
the added heat associated with elevated levels of GHGs in the atmosphere since 1998 is equivalent to the detonation of 2.74 billion Hiroshima size atomic bombs. Currently, heat equivalent to four such bomb detonations is being added each second. Ten bombs per second of heat is projected to be added later this century, in the absence of serious global mitigation efforts. Figure 5 (Cook, 2017) illustrates the impacts of all this heat being added to the atmosphere. More heat means both higher temperatures in the atmosphere as well as greater rates of evaporation, yielding more flooding rains. The impacts of higher temperatures and greater evaporation rates are depicted in Figure 5. They include: More intensive heat waves and drought, potentially threatened food supplies, greater risk of wild fires, melting ice yielding seawater rise and more intense weather events, such as more dangerous cyclones. The ocean’s ecosystems are also at risk due to a combination of ocean wanning and acidification, since about 90% of all the heat and 25% of the CO, ends up in the oceans. CO, absorbed in the ocean generates carbonic acid which increases the ocean’s acidity.
As Figure 2 illustrated, we face the prospects of wanning at the 4 °C level later this century. Warren
(2010) summarized the implications of a 4 °C warmer world as follows: “Enormous adaptation challenges in the agricultur al sector, with large areas of cropland becoming unsuitable for cultivation.... large losses in biodiversity, forests, coastal wetlands... supported by an acidified and potentially dysfunctional marine ecosystem. Drought and desertification would be widespread, with large numbers of people experiencing increased water stress. ... Human and natur al systems would be subject to increasing levels of agricultural pests and diseases, and increases in the frequency and intensity of extreme weather events.”
There is the Danger of a Runaway Situation if Warming occurs Too Rapidly and Activates Tipping Points Associated with Amplifying Feedbacks
It is important to note, that current projection models do not account for the possibility that there could be accelerating wanning due to “tipping points” associated with driving forces that could yield a point in time when the global climate changes from one stable state to another, a threshold which reaches a point of “no return” that can change the planet irreversibly. Such points could cascade, yielding a “hothouse Earth”. Figure 6 (an updated/upgraded figure from Climate Change Knowledge (2014)) illustrates the
Figure 6. Amplifying feedbacks could yield “runaway” warming.
relationship between GHG emissions and potential impacts with a focus on Amplifying Feedbacks. Examples of such feedbacks, that if cascaded could contribute to such a runaway state include:
A recent study (Steffen, 2018) examined this issue and concluded that potential planetary thresholds yielding accelerating and potentially irreversible warming could occur at a temperature rise as low as
2.0 °C above preindustrial levels. They concluded that limiting warming to a maximum of 1.5 °C would dramatically lower the risk of this potentially catastrophic instability'.
Although not discussed in the study, it follows that warming in the vicinity of 3-4 °C would substantially raise the probability of such tipping points, yielding a “hothouse earth”.
Growing Global Emissions, the Result of a Growing Population Demanding an Expanding Array of Resource Intensive Goods and Services
The dramatic growth in GHG emissions since the industrial revolution are driven by two key drivers. First, world population has been growing relentlessly'. World population is now at 7.5 billion, has tripled since 1950, and is expected to grow to over 9 billion by 2050. Second, in developed nations, people have expanded their list of “needs” to include personal transportation, residences with energy-intensive heating, cooling, and lighting, a diet heavily oriented toward meat consumption, and an ever-growing array of consumer goods and sendees. Developing countries are moving in the same direction, albeit at earlier stages. World population has been growing annually at about 1.2% and CO, emissions at 2.3% over the last 17 years.
Figure 7 illustrates the factors responsible for the challenges to long term sustainability with a focus on climate change, the most serious sustainability threat. The middle of the figure indicates that these human needs are met by means of a large array of industrial, agricultural, and energy technologies and
Figure 7. Drivers yielding GHG emissions and the two key mitigation approaches.
practices. Although, there are a multitude of sustainability impacts associated with these “technologies and practices”, independent of climate change. The major threats are shown color coded in two categories: Earth and Societal impacts. These include, degradation of air and water quality, depletion of minerals and fresh water supplies and ecosystem damage. Unique climate change impacts are listed on the right side of the figure and include: Potential food scarcity, infrastructure damage, mass population displacement and extreme and damaging weather events. As indicated by the red return arrows, in addition to such unique impacts, climate change has the potential to exacerbate impacts associated with other human activities, such as ocean and forest degradation. The bottom of the figure indicates that there are two classes of mitigation opportunities. The most commonly considered approach is replacing/upgrading current technologies and practices. Another, less discussed, but potentially important if technology modifications alone are insufficient to avoid serious climate impacts, would be to modify social and cultural behavior toward energy-efficient and resource-intensive lifestyles.