You write that “one potential response would be to adopt a new legal rule prohibiting the targeting of chemical facilities, because of the environmental harms likely to result.”

At least three rules of international humanitarian law (IHL) already deal with the issue. First, article 35 of the first additional protocol to the 1949 Geneva Conventions contains the basic rules on the means and methods of warfare and prohibits “to employ methods or means of warfare which are intended, or may be expected, to cause widespread, long-term and severe damage to the natural environment.” In addition, Article 55 contains the protection of the natural environment as it relates to the health and survival of the population. It demands that “care shall be taken in warfare to protect the natural environment against widespread, long-term and severe damage. This protection includes a prohibition of the use of methods or means of warfare which are intended or may be expected to cause such damage to the natural environment and thereby to prejudice the health or survival of the population.”

The problem of targeting chemical factories may arguably also be covered by Article 56 of the First Additional Protocol to the Geneva Conventions. It stipulates that “works or installations containing dangerous forces, namely dams, dykes and nuclear electrical generating stations, shall not be made the object of attack, even where these objects are military objectives, if such attack may cause the release of dangerous forces and consequent severe losses among the civilian population.” (However, the Commentary of the ICRC mentions that the drafters did not agree to include other installations than the examples listed in the article; in which case the problem of chemical factories would be covered by the two previously mentioned articles.)

The text of the first additional protocol can be found here: http://www.icrc.org/ihl.nsf/7c4d08d9b287a42141256739003e636b/f6c8b9fee14a77fdc125641e0052b079

The US and a number of other states have not ratified the first additional protocol to the Geneva Conventions. However, these principles have been identified to be part of customary law. The ICRC Study on Customary Humanitarian Law lists state practice and opinion juris to establish that the prohibition of the use of methods or means of warfare that are intended, or may be expected, to cause widespread, long-term and severe damage to the natural environment to be part of international customary law applicable in both international and non-international armed conflicts. According to the study, the natural environment is thus considered to be a civilian object and as such it is protected by the same principles and rules that protect other civilian objects (principles of distinction and proportionality and the requirement to take precautions in attack). This means that no part of the natural environment may be made the object of attack, unless it is a military objective, and that an attack against a military objective which may be expected to cause incidental damage to the environment which would be excessive in relation to the concrete and direct military advantage anticipated is prohibited. The ICRC also pointed out that the ICJ in the Nuclear Weapons Opinion, for example, the International Court of Justice stated that “States must take environmental considerations into account when assessing what is necessary and proportionate in the pursuit of legitimate military objectives.”

Your reference to the principle of proportionality is thus highly relevant. At the same time, before any analysis of proportionality is made, one must first establish that the objective is indeed a military objective. Only then, the twofold considerations of a) proportionality and b) precautions in attack come into play. If an objective is not a military objective, the attack is in any event unlawful.

I agree with you that having legal norms on the protection of the environment in wartime is clearly not enough. But before establishing new rules, insisting on the existing rules and disseminating them would be a necessary first step.

Thanks for your input on this issue; I am looking forward to your updates.