Development Plans must mitigate against climate change

I wonder how many people involved in the planning system are aware of the insertion by the Planning Act 2008 of  182 .Development plan documents: climate change policies into 19 of PCPA 2004 (preparation of local development documents) after subsection (1), the following apparently innocuous clause?

“(1A)Development plan documents must (taken as a whole) include policies designed to secure that the development and use of land in the local planning authority's area contribute to the mitigation of, and adaptation to, climate change.”(emphasis added)

I1S. 182 in force at 6.4.2009 for E.W. by S.I. 2009/400, art. 3(e)

http://www.legislation.gov.uk/ukpga/2008/29/section/182

I think that we were excused in overlooking this provision (and I include myself) as this did not prove very easy to find and does not appear to have been applied by those making plans or those engaged in their examination.  I don't think that the examiner to whom I have recently been giving evidence (who seems to be very experienced and knowledgeable) had ever had to consider whether a local plan had been compliant with this legal requirement (note the word "must"). It was disappointing that he seemed to be looking for wriggle room in respect of s39(2) of the same Act despite a clear absence of evidence that the Plan in question would contribute to the achievement of sustainable development.

In this recent case the council's sustainability appraisal had noted that almost all the policies and proposals would have 'minor negative' impacts in respect of carbon emissions with no 'major positive' to result in mitigation of any kind, let alone the level required by the Climate Change Act  and 4th/5th carbon budgets.  Why should there be any concern that the inspector will find some line of reasoning to argue that a development plan that proposes 40% growth and jobs implying probably the same growth in carbon emissions (if not more, due to added  congestion on the roads) would be  'sound'?  

The first reason is that, in the absence of an adopted plan, there is a concern that unplanned for sites will continue to be permitted in the absence of a 5 year land supply.  Whilst this should not matter hugely if such developments were genuinely sustainable in accordance with the presumption  in the NPPF,  there is a general understanding that inspectors (and LPAs) have been approving developments that fall a long way short of any reasonable measure of sustainability.

The second reason is that the inspector might find it difficult to find a plan to be unsound on grounds based on s19,  fearing a legal challenge from the LPA and/or concern from HQ that this would set a precedent for the preparation for all plans to effectively mitigate carbon emissions! However, the QC representing the LPA made no attempt to rebut the assertion of unsoundness on this legal ground and the development industry would be unlikely to challenge due to the benefits derived in the no-plan world. 

Where a point is arguable (although I can't see that the plan in question meets the s19 test) wouldn't it be better for decision-makers to err on the side of those seeking to protect the environment, leaving the spoilers the opportunity to challenge, rather than vice versa?