The American Geophysical Union (AGU) has a position statement on human-induced climate change of which Judith Curry was harshly critical. Roger Pielke Sr has pubished a dissenting view. If it is indeed so appalling, I thought I might work through it to find out what is wrong with it.

I’ll start at the beginning and work through it paragraph by paragraph.

Human activities are changing Earth’s climate. At the global level, atmospheric concentrations of carbon dioxide and other heat‐trapping greenhouse gases have increased sharply since the Industrial Revolution. Fossil fuel burning dominates this increase. Human‐caused increases in greenhouse gases are responsible for most of the observed global average surface warming of roughly 0.8°C (1.5°F) over the past 140 years. Because natural processes cannot quickly remove some of these gases (notably carbon dioxide) from the atmosphere, our past, present, and future emissions will influence the climate system for millennia.

Nothing really wrong with this. Atmospheric CO 2 has indeed increased sharply since the industrial revolution, we are responsible for this increase, and most of the observed increase in global surface temperature is probably anthropogenic. Atmospheric CO 2 concentrations will likely remain enhanced – relative to pre-industrial levels – for thousands of years.

Extensive, independent observations confirm the reality of global warming. These observations show large‐scale increases in air and sea temperatures, sea level, and atmospheric water vapor; they document decreases in the extent of mountain glaciers, snow cover, permafrost, and Arctic sea ice. These changes are broadly consistent with long‐ understood physics and predictions of how the climate system is expected to respond to human‐caused increases in greenhouse gases. The changes are inconsistent with explanations of climate change that rely on known natural influences.

Again, no real problems here. There are multiple, independent observations of changes that are consistent with what we would expect, and that are inconsistent with a pre-dominantly natural influence.

Climate models predict that global temperatures will continue to rise, with the amount of warming primarily determined by the level of emissions. Higher emissions of greenhouse gases will lead to larger warming, and greater risks to society and ecosystems. Some additional warming is unavoidable due to past emissions.

This all seems fine. We certainly expect global temperatures to – on average – continue rising and for the warming to depend largely on how much we emit. It’s also likely that the risks to society and ecosystems will increase with increasing warming. The only possible issue is the final sentence, which is not strictly true. If we were to halt all emissions now, we would expect warming – on average – to stabilise. That, however, is not going to happen, so it seems additional warming is essentially guaranteed.

Climate change is not expected to be uniform over space or time. Deforestation, urbanization, and particulate pollution can have complex geographical, seasonal, and longer‐term effects on temperature, precipitation, and cloud properties. In addition, human‐induced climate change may alter atmospheric circulation, dislocating historical patterns of natural variability and storminess.

One of the criticisms of the position statement seems to be that is hasn’t paid enough attention to regional effects. However, this seems like a perfectly reasonable comment about how we don’t expect the effects to be uniform in space and time.

In the current climate, weather experienced at a given location or region varies from year to year; in a changing climate, both the nature of that variability and the basic patterns of weather experienced can change, sometimes in counterintuitive ways ‐‐ some areas may experience cooling, for instance. This raises no challenge to the reality of human‐induced climate change.

Indeed. There are complexities that mean that the simple picture that is often painted isn’t going to be exactly right at all times and at all locations. That doesn’t mean that some event that appears to be at odds with what is simplistically expected due to anthropogenically-driven climate change provides a major challenge to our understanding of AGW. Of course, there will be many occasions where we’ll want to understand what has happened, but that doesn’t immmediately imply that we expect our basic understanding to be over-turned.

Impacts harmful to society, including increased extremes of heat, precipitation, and coastal high water are currently being experienced, and are projected to increase. Other projected outcomes involve threats to public health, water availability, agricultural productivity (particularly in low‐latitude developing countries), and coastal infrastructure, though some benefits may be seen at some times and places. Biodiversity loss is expected to accelerate due to both climate change and acidification of the oceans, which is a direct result of increasing carbon dioxide levels.

This is somewhat outside my area of expertise. However, if we do continue to emit CO 2 we’d expect warming to continue, the water cycle to change, and ocean acidification to continue. That this could lead to biodiversity loss, threats to public health, and have impacts with repect to agriculture, seems quite reasonable. As it says, however, there may be some benefits, but that doesn’t really negate that there will potentially be some severe negative impacts.

While important scientific uncertainties remain as to which particular impacts will be experienced where, no uncertainties are known that could make the impacts of climate change inconsequential. Furthermore, surprise outcomes, such as the unexpectedly rapid loss of Arctic summer sea ice, may entail even more dramatic changes than anticipated.

Actions that could diminish the threats posed by climate change to society and ecosystems include substantial emissions cuts to reduce the magnitude of climate change, as well as preparing for changes that are now unavoidable.

All seems pretty solid. There could be outcomes that are surprising and dramatic. If we want to reduce the risk of severe negative outcomes we will need to reduce emissions, utimately aiming to get them to zero, or close to zero. We will, however, also have to prepare for – and adapt to – changes that are probably now unavoidable.

The community of scientists has responsibilities to improve overall understanding of climate change and its impacts. Improvements will come from pursuing the research needed to understand climate change, working with stakeholders to identify relevant information, and conveying understanding clearly and accurately, both to decision makers and to the general public.

Yup, seems perfectly reasonable.

So, I’m not really seeing a problem with this. It seems predominantly evidence-based and certainly doesn’t seem to take a position that is somehow inconsistent with the available evidence. Maybe the one criticism could be the title:Human‐Induced Climate Change Requires Urgent Action. This is a bit definitive and maybe one could argue that it should have been more along the lines of If we want to reduce the risks associated with …..”. However, I think it is now so widely accepted that it requires action that this seems a bit like a nit-pick. If others disagree, or can find something wrong with the position statement, let me know in the comments.