Increasing Lightning Frequency yet another negative feedback hypothesis in a changing climate, by Dr Chris Barnes, Bangor Scientific and Educational Consultants LL572TW. E-mail doctor.barnes@yahoo.co.uk

Abstract

Any estimates of how much or how little warming and other manifestations of climate change such as extreme weather can only be as good as the current mathematical model. If there are feedbacks in nature that are not in the model either because they are not known about or are too complex to accommodate then the model will be of little or of limited use. The present article presents a new hypothesis to show that following short term warming, lighting frequency increases and furthermore by means of NOx injection at a variety of atmospheric height levels will actually, as a result or more than one type of atmospheric chemistry and microphysical interaction, bring about climate cooling rather than the rather more perhaps first sight ozone driven and intuitively expected warming scenario.

Introduction

There is no doubt that global climate is changing and that both solar changes and anthropogenic drivers have their parts to play in causation.

Global climate change, however, is exactly that. It does not necessarily have to equate with runaway global warming. Indeed in recent years global warming per se has actually reached a plateau causing revised and lowered estimates for the future. Such an unexpected slowing in the warming rate may be because of unforeseen or unexpected climate (albedo) negative feedback mechanisms which have somewhat of a time lag before becoming operative. Such new feedback mechanisms are not of course entirely unknown, see for example, Kulmala et al who discuss a new feedback mechanism linking forests, aerosols, and climate.

Any estimates of how much or how little warming and other manifestations of climate change such as extreme weather can only be as good as the current mathematical model.

If there are feedbacks in nature that are not in the model either because they are not known about or are too complex to accommodate then the model will be of little or of limited use.

One such feedback that climate scientists are only just beginning to consider is lightning. It is well know that climate change models predict more storminess, but do they predict more lightning? If so does it really matter? Fortunately, lightning is a weather feature which can either be measured by observation or by several types of direct and indirect instrumentation.

The purpose of this present article is to show that following short term warming, lighting frequency increases and furthermore by means of NOx injection at a variety of atmospheric height levels will actually, as a result or more than one type of atmospheric chemistry and microphysical interaction, bring about climate cooling rather than the rather more perhaps first sight intuitively expected warming scenario.

Increasing thunderstorms or increasing lightning?

Thunderstorms are due to convection: Heating of Earth's surface by sunlight and infrared radiation causes water to condense as buoyant air rises. When updrafts are vigorous, water drops are carried above the freezing level, a necessary ingredient for lightning. Theoretically, as CO₂ increases the land surface warms, making stronger updrafts that are more likely to produce lightning. In a doubled CO₂ climate, one model estimates that the western U.S. will see fewer lightning storms overall, but 25% more of the strongest storms, with a 5% increase in lightning, see http://www.giss.nasa.gov/research/briefs/delgenio_07/.

http://www.sciencedirect.com/science/article/pii/S0169809508002214 also concludes that a warmer future should see more lightning activity due to 'more explosive' storms.

One theoretical study produced results predicting that a change in the average land wet-bulb temperature of the globe of just 1K would result in a change in lightning activity of about 40%, see N Reeve, R Toumi - Quarterly Journal of the Royal …, 1999 - Wiley Online Library

Thus the consensus would appear to be that whether or not we see more storms there would always be more intense lightning or simply more lightning.

Lightning NOx Hypothesis of Global Cooling

Since NOx from lightning storms has never before been considered in a global cooling or negative feedback situation, I shall borrow knowledge from the behaviour of anthropogenic Nox. Wild et al ( 2001) http://onlinelibrary.wiley.com/doi/10.1029/2000GL012573/pdf

conclude that anthropogenic emissions of short-lived, chemically reactive gases, such as NOx and CO, are known to influence climate by altering the chemistry of the global troposphere and thereby the abundance of the greenhouse gases O3, CH4 and the HFCs. There study used the characteristics of the natural modes of the tropospheric chemical system to decompose the greenhouse effect of NOx and CO emissions into (i) short-lived modes involving predominantly tropospheric O3 and (ii) the long-lived mode involving a global coupled CH4-CO-O3 perturbation. They then combined these two classes of greenhouse perturbations—large, short-lived, regional O3 increases and smaller, long-lived, global decreases in CH4 and O3—and found that most types of anthropogenic NOx emissions lead to a negative radiative forcing and an overall cooling of the earth.

This is probably yet another reason why in some circumstances, increased air traffic seems to be bringing about cooling rather than warming, see also Barnes ….

Lightning storms are known to generate NOx over a range of atmospheric heights because of cloud to ground and cloud to cloud discharge. The maximum probability of finindg lightning NOx is at heights of 1-5.55 Km in the troposphere, see LE Ott, KE Pickering, GL Stenchikov… - Journal of …, 2007 - Wiley Online Library, and between 8 and 10.5 km, lightning NOx  actually causes decreased net ozone production. This is more or less substantiates the earlier findings of Wang et al, Atmos. Chem. Phys., 4, 557-562, 2004 www.atmos-chem-phys.net/4/557/2004/

Taking the fact then that estimates of NOx production from lightning storms are of the same order of magnitude as anthropometric production if not slightly lower ( 5-20Tg per annum versus 36 Tg/annum, see Price et al 1997, there is no reason whatsoever to suppose that increased lightning in a warmer world could not and indeed is not already producing climate negative feedback and some degree of stabilisation against runaway global warming.

The outcome of other tropospheric chemistry approaches is further that NOx enhancement has a notable effect on modelled hydroxyl-radical concentrations. In particular, such increases in hydroxyl-radical burden would be expected to reduce the atmospheric lifetimes of reactive greenhouse gases—such as methane—as well as to increase aerosol production rates and cloud reflectivity, therefore exerting another mode for cooling influence on the climate.

Toumi et al (2012) have discussed lightning only in terms of ozone production and naturally reach the opposite conclusion to that reached here.

Summary

Runaway global warming presently does not seem to be happening. Climate models are only useful if they contain all known feedbacks and climate mechanisms are notorious for non-linearity.

This brief paper advance a new hypothesis that in a warmer world increased lightning intensity will produce more NOx and hydroxyl radicals, therefore climate cooling. Further work is needed to test the hypothesis.