Climate change is a security issue.

Firstly security issues can also be defined as being a threat to a persons way of life or existence that demands urgent priority and near immediate action to be taken regardless of whether military action is used or not.The opposition in this case is taking what could be described as a classical Realists view of security where the only threat that can be treated by. This something that has been criticised by a number of theorists such as Ken Booth, Jessica Matthews and Barry Buzan as being too narrow

Secondly For some states like the Maldives which are at risk of literally going underwater (well mostly) climate change may represent precisely the form of threat which requires a form of military action whether it is covert or overt. Just because smaller states or developing world states do not have the capabilities to launch an attack doesn't mean that military action should be discounted entirely.

Security issues are issues of war and peace which are likely to involve military action, whether this be a full scale war or counter insurgency. insurgency, something that is normally a last resort. Also military action normally follows a period where sanctions have been applied such as the invasion of Iraq.  
 
Climate change is however really an issue for regulation of emissions, environment agencies and other internal departments. Like the financial crisis it involves large amounts of money and requires action but this does not include any militry response; Britain did not invade Iceland just because some government money was in an Icelandic bank when the economy crashes. crashes.