So what happens if we finally get all the climate policies into action, cut down carbon emissions, sign a global agreement etc and then Mother Nature throws us severe droughts, floods and other major natural disasters anyway? Why work hard to fight man-made climate change if natural climate change is going to continue regardless? It’s a fair question, so we put it to some climate scientists.

And today’s answers even involve a dash of polite disagreement. It’s like watching the peer-reviewed method in action.

Got a question about climate science? Right now at Rooted we’re running the Ask a climate scientist series. Keep the questions coming as well, by emailing me directly.

These answers are coming from American Geophysical Union’s Climate Science Q&A service, where more than 700 volunteer scientists provide factual and peer-reviewed climate science information to journalists. The AGU only comments on science, not climate policy.

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Crikey reader Martin asks:

“We’re often told of the severe consequences of human induced climate change — but if climate change is bad, isn’t natural climate change just as dangerous? What are the chances of us mitigating the human induced aspects, only to then be hit with some unforseen natural event (the ‘climate surprises’ that the IPCC talks of) and still have to face serious consequences?”

Vincent P. Gutschick, director of Global Change Consulting Consortium Inc., responds:

“Bad” is a value judgment, assessed differently by various persons, organizations, and enterprises. We may rephrase the question to focus on changes per se and pass the findings on to stakeholders and policymakers.

That said, there is a spectrum of change. Climatic means in temperature, precipitation, storm activity, and such have impacts, but extremes may be more important in very many issues. These extremes includes floods, severe storms, and sudden temperature shifts, among others. Extremes can occur on long time scales, too.

The rise in atmospheric CO2 alone directly impacts plants, wild and agricultural, changing their photosynthetic rates, water-use efficiency, protein content, and more. It also acidifies oceans and threatens the persistence of coral reefs. The current rate of increase in CO2 exceeds all past events and is projected to have major effects on the performance, competitiveness, and geographic distribution of plants.

In quantifying change, we need to distinguish changes in fundamental drivers (greenhouse gases, solar activity, parameters of the Earth’s orbit, volcanic activity) from amplifiers, modulators, and ultimate responses such as precipitation and temperature regimes, atmospheric and oceanic circulation patterns, CO2 balance of oceans and vegetation, etc.

Focusing on the fundamental drivers, there are natural and anthropogenic (human-caused) changes. Take the natural changes: we know of ranges, rates of change, and recurrence times, if imperfectly (orbital changes are well known, solar changes less so, volcanism poorly so). We also know something of the amplifying factors (e.g., ice albedo as an amplifier of radiative trapping) and of ultimate effects (e.g., oceanic temperatures), more imperfectly. Furthermore, we know that some anthropogenic changes lie outside the bounds of past natural changes – specifically, the rate of rise of atmospheric CO2, as well as deforestation rates that affect the absorption of solar radiation and the cycling of water (the part going through plants) in the atmosphere.

The potential for anthropogenic changes to exceed the bounds of natural changes is raised by the multiplicity of changes caused by humans, such as never have occurred in Earth’s history. Simultaneously, we are changing greenhouse gas concentrations, land cover, atmospheric aerosol concentrations (by burning biomass, esp.), ozone concentrations at the surface and in the stratosphere, reactive nitrogen concentrations on land and in waters (e.g., fertilizer runoff in rivers leading to algal blooms and then dead zones in coastal waters), and so on.

We need to be prepared for both natural and anthropogenic changes, by acquiring knowledge about the changes and their effects. The imperfection of our knowledge about natural changes alone is daunting and it’s demanding of research ranging from understanding causes to preparing for effects. When we add in the imperfection of our knowledge about anthropogenic effects, the challenges are much greater. We certainly cannot reduce concerns about these with the idea that natural changes are occurring anyway.

Jim Bouldin, research ecologist at the University of California at Davis, adds:

Vince’s answer is great. I’ll add a couple points to it.

A lot could be said here. Although a given amount of radiative forcing will have the same temperature effect on the planet regardless of whether humans produced it or not, the primary human forcings (greenhouse gases and aerosols) have other effects that, for example, a change in solar irradiance, would not have. For example, CO2 acidifies water bodies and changes plant physiology in certain plant groups, and aerosols can cause human health problems, etc.

As for “surprises”, much of the discussion around that topic by the IPCC, in my reading, deals with surprises in response to the GHG forcing we are imposing–not just any random surprises out of the blue. That is, it’s really hard to predict certain phenomena in a strongly forced system, as the climate system now is, that would not be so difficult if the system were not under the forcing. Ice sheet melt rates, and elements of the carbon cycle, for example.

As for the idea that some “unforseen natural event” could come along and negate all GHG mitigation efforts, it is difficult to imagine what that could be. It would have to equal the current CO2 radiative forcing increase from pre-industrial (about 1.8 Watts/square meter), which even if emissions were cut to zero tomorrow, would remain in effect for many decades because of it’s long atmospheric lifetime.

You also have to factor in to your equation what the surprise’s effect would be if you hadn’t mitigated any GHGs, that is to say, the cumulative effect of the two, which would almost certainly be worse than either alone.

Ellen Thomas from Yale University adds a little more (I’ve included all answers in full for transparency):

I agree that Vince’s answer is very good. As a paleo-research worker I often get the question – “so if climate change occurred naturally, what’s so bad or dangerous about future global warming?” I always answer that there is nothing ‘bad’ about it for Earth or Nature or anything like that, the ‘bad’ or ‘dangerous’ would be only from the point of view of human civilization — as someone from the Netherlands, I’d argue that there is nothing intrinsically bad about sea level rise, but sea level rise by a few feet would pose major (and financially severe) problems for Dutch society.

I do not quite agree with one sentence in the response by Vince “Furthermore, we know that some anthropogenic changes lie outside the bounds of past natural changes”. For this one would have to define ‘past’ — for someone like me who works on time scales of millions of years I would not want to make that argument — atmospheric CO2 levels, for instance, were probably much higher than what we foresee for the next several centuries if we go back far enough in earth history. What may be “outside the bounds of past natural history” are the rates of changes, e.g. the rate of input of CO2.

As to surprises; again, as someone working in ‘deep time’ — of course there may be surprises: an mega eruption of Yellowstone or an asteroid impact and other extremes that happened in the past. But as to such onforeseen events, I agree with Jim that “what the surprise’s effect would have been if you hadn’t mitigated any GHGs, the cumulative effect of the two, would almost certainly be worse than either alone”.

The actual ‘surprises’ mentioned by IPCC, however, are not such extremities, but refer more to non-linear pocesses, tipping points and threshold effects, such as the West Antarctic ice sheet (which is marine based) detaching from its base to some large extent, then floating to lower latitudes and rapidly metling, or major release of methane from melting permafrost.

In such cases the last sentence ”what the surprise’s effect would have been if you hadn’t mitigated any GHGs, the cumulative effect of the two, would almost certainly be worse than either alone” is still valid.

I subscribe to Crikey because I believe in a free, open and independent media where news and opinions can be published that I can both agree with and be challenged by.

As a Crikey subscriber I always feel more informed and able to think more critically about issues and current affairs – even when they don’t always reflect my own political viewpoint or lived experience.

Jess
Singapore

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