It looks like climatologists could learn some lessons from salt. A recently concluded massive study on the effects of salt in the human diet found that — contrary to public perception — in people at risk for heart disease, less salt was not always more beneficial. A moderate amount of salt, scientists now say, is better than high or low intake, contrary to longstanding belief.The human body is a very complex system that constantly perplexes and challenges established assumptions and scientific hypotheses. Our understanding of health and nutrition is constantly changing as we find out more about our own anatomy and our biochemistry, but that is a good thing.However, complicated systems are hard to understand. In my lifetime there have been many dramatic reversals on questions of nutrition and health. The scientific consensus of one decade is often the old wives’ tale of the next.The world’s climate system is complex. Global climate has varied tremendously over millions and billions of years, and our study of this system is still in its infancy. It is likely (though nothing is certain) that there will be many shifts in the way we understand things as we gradually work our way toward a clearer and more detailed understanding.This makes the hacktivists unhappy: they desperately need a clear and “settled” scientific consensus because the policy proposals they have are so sweeping and expensive that only overwhelming evidence can make a plausible case for them. More than once, green advocates have given in to the temptation to be “clearer than truth” on climatology. Over time, this has reduced public confidence in climatology itself as well as in the motives and wisdom of the green lobby.While the science behind climate change has a stronger foundation than many skeptics accept, its conclusions and forecasts are less credible than the hactivists allege. But as the latest tweak to the salt and health consensus — to say nothing of the evidence now suggesting that CO2 may have less effect on temperature than many have thought — demonstrate, climate policy cannot depend on an over-rigorous insistence on the absolute nature of what will remain for some time a shifting scientific foundation.