A 2 °C warming (one more degree than where we are today) would put 20-30% of the world at risk of desertification and drought by 2050. The regions that will be most affected by an average temperature increase are those located in Central America, Southeast Asia, Southern Europe, Southern Africa and Southern Australia. Only 7-10% of the world would be at risk of desertification and drought by 2050 if we only warm by 1.5 degrees (0.5 degrees from where we are today).
The world will probably wait for the 10% desertification to happen. There have been recent adjustments as to when the 1.5-degree warming would happen. There were papers that indicated 1.5-degree warming was delayed by 20 years. If other climate researchers are not adjusting then they would be claiming that 1.5-degree warming has already occurred. The world would have to rapidly get to zero emissions to avoid 2-degree warming.
There are plenty of countermeasures at the point when the effects become unambiguous. Prior to unambiguous effects, there have been a lot of uncertainty and guessing on climate. It is difficult to base multi-trillion plans on that level of uncertainty.
Aridity—the ratio of atmospheric water supply (precipitation; P) to demand (potential evapotranspiration; PET)—is projected to decrease (that is, areas will become drier) as a consequence of anthropogenic climate change, exacerbating land degradation and desertification. However, the timing of significant aridification relative to natural variability—defined here as the time of emergence for aridification (ToEA)—is unknown, despite its importance in designing and implementing mitigation policies. Here we estimate ToEA from projections of 27 global climate models (GCMs) under representative concentration pathways (RCPs) RCP4.5 and RCP8.5, and in doing so, identify where emergence occurs before global mean warming reaches 1.5 °C and 2 °C above the pre-industrial level. On the basis of the ensemble median ToEA for each grid cell, aridification emerges over 32% (RCP4.5) and 24% (RCP8.5) of the total land surface before the ensemble median of global mean temperature change reaches 2 °C in each scenario. Moreover, ToEA is avoided in about two-thirds of the above regions if the maximum global warming level is limited to 1.5 °C. Early action for accomplishing the 1.5 °C temperature goal can therefore markedly reduce the likelihood that large regions will face substantial aridification and related impacts.
As recently as 2014, the Intergovernmental Panel on Climate Change (IPCC) had indicated that there we would CO2 emissions would soon exceed the level where 1.5-degree Celsius warming over the industrial (1870) level would occur.
The Mercator Group has an online countdown clock based on the IPCC, Climate Change 2014: Mitigation of Climate Change. The contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.
The top left of the clock you can select, for reaching the 2°C target, an optimistic upper estimate (about 940 Gt¹ remain in the budget), a medium estimate (about 760 Gt² remain), or a pessimistic lower scenario (about 390 Gt¹ remain). The right of the screen shows the scenarios that would correspond to the 1.5°C target. The calculation is based on the assumption that annual emissions remain at the level of 2014; while between 2000 and 2010, an annual growth of greenhouse gas emissions of 2.2% has been observed.
Based on the IPCC 2014 and the countdown clock we had already run out of time on the 1.5C warming low probability and next year the 1.5C medium probability clock would have run out.
Re-estimating the remaining carbon budget
This was cutoff as feature image. The amount of CO2 emissions at 40 billion tons per year out to 2100 shows warming at about 1.7 degrees. 0.2 degrees was added with shift from 30 billion tons per year to 40 billion. It takes more CO2 to force up the same level of temperature increase. CO2 is logarithmically correlated to temperature increase. So If 40 billion tons per year is 1.7 degrees then to get the next 0.3 degrees would probably be about 70-90 billion tons per year out to 2100.
In their paper, they ask a different question of these ESMs, namely what is the cumulative CO2 emissions budget, from today onwards, compatible with levels of simulated warming on top of the model’s present warming?
In other words, if human-caused warming over this decade was – on average – about 0.9C, a budget for 1.5C above preindustrial corresponds would correspond to a budget for 0.6C more human-caused warming from this decade on.
We investigated what ESMs can tell us about such budgets. This approach allows us to examine what the models say about future warming relative to future emissions, without bringing in any potential model bias simulated over the historical period.
This method gives an estimate for the remaining 0.6C of warming of about 880bn tonnes of CO2, from the beginning of 2015. This is about equal to about 20 years at current annual emissions, or alternatively, a straight line decrease in CO2 emissions from today’s values to zero in about 40 years.
They construct pathways in which emissions are continually adapted over time in order to actually achieve a warming of 1.5C in 2100 no matter what the climate response turns out to be. This mimics an adaptive climate policy under the Paris Agreement’s pledge-and-review system – and assumes it’s successful.
Estimated in this way, we find the remaining carbon budget for a 66% probability of limiting warming to 1.5C in 2100 is 915bn tonnes of CO2 (from the start of 2015). This number is consistent with our ESM estimates given earlier, and again assumes very aggressive action to reduce non-CO2 contributions to warming.
Old Upper limit on 2-degree warming has become the lower or middle limit for 1.5-degree warming
I think it also means that just hold steady on emissions would mean no 2-degree warming this century.
The previous estimates of the amount of CO2 that could be released before world temperature rose to 1.5C above pre-industrial levels was 70 billion tonnes of Carbon after 2015 but a reassessment allows for a “carbon budget” of another 240 billion tonnes of emissions before 1.5C above pre-industrial levels.
In a 2014 report, the UN’s Intergovernmental Panel on Climate Change (IPCC), said the carbon concentration in the atmosphere should not exceed 450 parts per million (ppm) of CO2 equivalent (CO2eq) by 2100 for a “likely”, 66-percent, chance of 2 C. According to the IPCC report, the concentration in 2011 was already 430 ppm CO2eq. On the basis of the IPCC figures, a budget of 400 billion tonnes was calculated as the maximum amount of CO2 humanity can emit into the atmosphere from 2011 and still keep the 1.5 C goal in sight.
For 2015, that number dropped to about 245 billion tonnes.
The new analysis, however, estimates the remaining budget from 2015 to be closer to 880 billion tonnes of CO2—nearly four times bigger than the UN estimate, the research team said.