2. Expansion of Key Climate Science in the AR5
Last time we ended with the IPCC’s “smoking gun” statement for the AR5:
“It is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together. The best estimate of the human-induced contribution to warming is similar to the observed warming over this period. {10.3}”
Understanding the administrative process is key to the bigger picture of the report, but this time I will be digging into the treatment of scientific data and models. By examining changes made to the timelines, climate simulation models, and consensus language from further climate study, we are provided with a framework for the IPCC’s report and consequently, its implications for the public and policymaking community.
What's New in the AR5 Report?
Timelines and Decadal Predictions
The first notable changes in the IPCC’s climate report are decadal models that correspond to long-term temperature and precipitation projections. These short-term models offer a focused counterpoint to data from models that span millennia and continents. With all of that data in one model, modelers take certain liberties and must assume some data, but it has been asserted that this might not lead to the soundest evidence (Lloyd &Parker). In their defense, predicting the weather next week is a challenge, so predicting it over hundreds of years is not for the faint of heart. That said, with the consensus of the public so skeptical, it is easy to understand why the IPCC decided to concentrate the data into these decadal predictions.
Due to the chaotic and changing nature of climate, it is difficult to model precise long term scenarios. The sporadic manner of both the observational data and the inferred starting points from proxy data over long-periods heavily rely on well-made algorithms and corrective functionality to make them reliable. Even with the technology and rigorous attention exact results are not guaranteed. It is a fact that the less accurate the data to start, the more inferences must be made. The advantage to short-term modeling is that it provides us with a more reliable and concise picture of a multi-faceted and global data set as well as a reference point with which to compare the long-term models. Chapter 11 deals with these predictions.
Time and temperature are but one study that can be made concise for further analysis; regional weather patterns, temperature, and precipitation all have an impact on these models.
Treatment of Regional Information
In the AR5, the IPCC took a closer look at key regional phenomena such as monsoons, El Niño, volcanic activity, and other localized forces that can decrease reliability of global models. “A phenomenon is considered relevant to regional climate change if there is confidence that it has influence on the regional climate and there is confidence that the phenomenon will change, particularly under the Representative Concentration Pathway 4.5 (RCP4.5) or higher end scenarios. {Table 14.3}
The data collected from these events is taken into account and modeled to compare with global changes, as well as explain some of the regional climate variability found in the more comprehensive climate models. It was found that several weather events do impact these models and as such the IPCC can course-correct on future calculations.
Note that in North America as well as Asia, the effects of El Niño (ENSO) heavily influence precipitation. Temperature is set to rise with variability across regions. Information found in Chapter 14 is of specific interest to policymakers concerned with regional information. Additionally, there is an Atlas of Global and Regional Climate Projections “to enhance accessibility for users and stakeholders and ease the hand-over of relevant information from WG I to WG II. (Meehl)”
Expanding the Scientific Scope
Other improvements to the IPCC report include an assessment of the science of clouds and aerosols including a section on Geoengineering to counteract climate change and its possible effects (pg. 648). It also includes and an end-to-end assessment of the carbon cycle (e.g. ocean acidification, feedbacks). Also, biogeochemical cycles and carbon cycles are featured more prominently in the AR5. Figure 6.1 from Chapter 6 of the IPCC report shows a schematic of the carbon cycle that is just one of several helpful illustrations in that chapter. Although there are many interesting changes to some of the more analytical aspects to the AR5, for the sake of time and space (and the fact that it is integrated into one bigger picture) I will not get in to the details, but will recommend at least a quick read of the summaries on chapters 6, 7, and 13.
Improvement of Models
“Of the roughly 45 “standard” models in the Coupled Model Intercomparison Project phase 5 (CMIP5) database assessed in the AR5:
· 14 are “high top” with a resolved stratosphere (only 1 in CMIP3)
· 19 are “Earth System Models” with at least interactive ocean biogeochemistry (none in CMIP3)
· Most have some kind of prognostic aerosol formulation and can simulate direct and indirect effect (very few included prognostic indirect effect in CMIP3)
· None use flux correction (about a third of the models in CMIP3 used flux correction)”
It was mentioned earlier that some modeling done on climate change has been called into question for its validity given the ambiguous starting points for data as well as inconsistent temperature readings in former years. The IPCC has responded to that in their treatment of the models in the AR5. This can be illustrated most clearly with RPC’s or (Representative Concentration Pathways). RPCs are projections of climate change scenarios that have been modeled by the IPCC, three of which are mitigation scenarios. The IPCC has said their modeling has improved in terms of capability.
RPC 2.6 was designed to keep global warming to less than 2 degrees centigrade below pre-industrial (in that case, you need negative emissions). This means pulling more CO2 out of the air than is put in.
The most controversial data in study can be found in Chapter 12. The surprise (or maybe it is no surprise) here is the discovery that the high CO2 concentrations causing global warming will persist for centuries. Even if you drop emissions to 0, the concentrations (and temperatures) will remain the same for about 300 years.
It is clear from the graphic labeled atmospheric CO2 that there is a linear relationship between concentrations, emissions, and temp increases. It was said in the CIRES seminar that in light of these correlations, developed countries tried to look for wiggle room and developing countries were on board.
What are the Implications of New Climate Information?
So what do all these graphs mean, and why should you care? I got one answer in the CIRES seminar on the IPCC report from Linda O Mearns. She brought up an important point when she asserted that one question raised in this fifth report is “If our understanding of the climate system has increased, why hasn’t the range of temperature predictions been reduced? - FAQ 1.1 PG 156
It seems a fair question to ask since most of these models look much fatter than they should given the amount of information we have to predict changes in climate. There are a few reasons for this:
- Natural variability is not something that can be reduced
- Future emissions and concentrations of greenhouse gasses are unknown, and our response to those scenarios is not known (it is difficult to predict human behavior)
- Climate response to concentrations might be reducible in variability but this will take time to monitor and adjust accordingly
Lastly, since socioeconomic changes are the hardest to predict, the IPCC has come up with some scenarios that may play out while we feel climate change effects in a special report. These Shared Socioeconomic Pathways (SSPs) are meant to find out how easy it would be to adapt to and mitigate climate change. They were described by Linda O Mearns, review editor for Working Group 1, "They form part of a new framework to facilitate production of integrated scenarios based on combinations of climate model projections (based on RCPs), socioeconomic conditions, and assumptions about climate policies."
The description of the SSPs (best case and worst case scenarios) are as follows:
SSP1- Sustainability- reduction of resource intensity and fossil fuel dependency, reduction in poverty, rapid technological change, high levels of education, low population growth
SSP2- Moderate- trends similar to the last few decades continue - slow decrease of fossil fuel dependency
SSP3- Fragmented World- regions of extreme poverty, pockets of moderate wealth, most of the world struggling, international trade severely restricted, population growth high
SSP4- Unequal World- small rich global elite responsible for a lot of emissions, development of alternative energy strategy controlled by elite. So low challenge for mitigation, but high for adaptation for global poor
SSP5- Conventional Development- oriented toward economic growth as solution to social and economic problems – energy systems dominated by fossil fuels, leading to high ghgs, thus challenge to mitigation
Each presents with a set of challenges wether it is high adaptation or low mitigation of climate change, but the IPCC is thinking not just about the science, but how it affects people. Several of the reports and supplementary materials can be found here.
With the world understanding climate science more than ever, and governments finally taking steps, it is tempting to see our SSPs as a 1 or 2 scenario, but there is more work to be done. It is clear from these climate change seminars that timelines are better specified which leads to a better understanding of what is coming. We know the scientific scope has expanded to include indirect contributors and measure their impact for a more reflective view of regional climate. It is also apparent that although there will always be some variability because of factors like natural weather and the unpredictability of humans, our models are improving with climate change understanding. We even now have a formulated metric for emissions scenarios that may play out in the future, helping our policymakers and leaders prepare for what's next, but as with many things, it is hard to know where you are going when you have yet to understand where you've been. In the next installment of my reports on the IPCC seminar, we will learn how the IPCC measures what happened thousands and millions of years ago, what is relevant about ice cores, and why they are so confident in their numbers. Stay tuned for Chapter 5, Paleoclimate.
