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New study: ‘Realistic’ global warming projections for the 21st century – ‘Realistic, non-alarming scenarios of 21st century climate’

New study:


“Realistic” global warming projections for the 21st century

by Nicola Scafetta

My new paper  demonstrates that realistic emissions scenarios and climate sensitivity values & scenarios of natural climate variability produce more realistic, non-alarming scenarios of 21st century climate.

I would like to thank Judith Curry for inviting me to write a short blog post on my just published paper:

Nicola Scafetta. Impacts and risks of “realistic” global warming projections for the 21st century. Geoscience Frontiers 15(2), 101774, 2024.

The paper is open access and, therefore, it is accessible to all.

I believe the work is significant because it addresses the central issue that is of general interest: how much warming can we expect in the 21st century? These are serious challenges that scientists must solve to truly assist policymakers. Is today’s climate alarmism founded on real science, or is it simply an extrapolated view based on flawed arguments?

Answering such a question defines the steps that must be taken to address any expected threats associated with possible future climatic changes. However, the uncertainties are so great that no consensus can be reached. Some argue that we are on the verge of a massive climatic disaster if net-zero emission policies are not imposed quickly, while others argue that nothing will happen. Technically, anyone can present arguments in support of his or her belief because of the large uncertainties surrounding these climate change issues.

I’ve opted to address the issue by highlighting recent research efforts to reduce uncertainties in order to obtain more “realistic” climate estimates for the twenty-first century. This might then be used to better analyze the actual impacts and hazards of climate change, with the hope that people will be able to agree on the best remedies.

I have identified four sources of uncertainties:

  1. Which shared socioeconomic pathway (SSP) scenario for the twenty-first century is most plausible? According to recent scientific literature, it is the SSP2-4.5 scenario, which is a moderate and pragmatic scenario in which CO2 emission rates maintain around present levels until 2050, then reduce but do not reach net-zero by 2100. Unfortunately, most of the climate alarmism is based on unrealistic scenarios like SSP5-8.5 and SSP3-7.0, which result in overestimation of future projected warming and greater alarm.
  2. How sensitive is the climate to CO2 increases? According to recent scientific research, the Equilibrium Climate Sensitivity (ECS) should be between 1 and 3 °C. Unfortunately, the IPCC AR6 relied heavily on Global Climate models with ECS ranging between 2.5 and 4 °C (likely range), which overestimates future projected warming.
  3. Can we rely on the warming presented by surface temperature records to calibrate and/or validate which models to use for climate projections? Addressing this point is critical because recent literature has suggested that surface temperature records may be significantly influenced by non-climatic warm biases (e.g. contamination from urban heat islands, among others), and because satellite-based lower troposphere temperature records (e.g. UAH-MSU v6 and NOAA-STAR v5) show a warming rate that is 30% lower than recent surface temperature records (as shown also by the IPCC AR6). The concern is that the models expect that the troposphere will warm faster than the surface, not less. As a result, the warming rate of surface temperature records should be questioned. In this case, all CMIP6 GCMs are running “too hot,” indicating a very low actual value of ECS (1-2 °C), implying that future climate change would be more moderate than projected by the IPCC in all cases.
  4. The fourth question is whether the GCMs accurately reflect natural climate change variability. The issue is significant since a vast body of research indicates that the CMIP6 GCMs are incapable of reproducing natural climate variability because they ignore multiple well-known climatic cycles at all time scales. There is a quasi-millennial climate oscillation with a likely solar origin that characterizes the entire Holocene and is responsible for the well-documented Roman and Medieval Warm Periods, which models are unable to reproduce (as timidly acknowledged by the IPCC AR6 figure 3.2). Other natural oscillations were also detected, such as the quasi-60-year oscillation seen in the Atlantic Multidecadal Oscillation signal, as well as many other oscillations classified as solar/astronomically driven in previous studies. While GCMs suggest that over 100% of the observed warming is manmade, these oscillations could have contributed significantly to the warming recorded in the twentieth century. Introducing cyclical natural variability predicts low ECS values (1-2 °C) and that the GCMs grossly underestimate the solar impact on climate.

Using the information discussed above, “realistic” climate change projections must be created using the SSP2-4.5 and: (1) only models with a low ECS (less than 3°C); (2) rescaling the models to the lower warming rate of the lower troposphere temperature records; and (3) adopting semi-empirical models of natural climate variability. As a result, in all three situations, the projected warming for the twenty-first century is congruent with the IPCC’s projected warming using the net-zero scenario SSP1-2.6. This is clearly demonstrated in the graphical abstract of my paper, which is displayed below:

Graphical Abstract

Because future climate change is expected to be modest enough that any potential related hazards can be addressed efficiently through effective and low-cost adaptation strategies, the 2.0 °C Paris-agreement warming target for the twenty-first century can likely be met even under the feasible and moderate SSP2-4.5 emission scenario without the need for implementing rapid, extremely expensive, and technologically likely impossible net-zero decarbonization policies.