In case there is global climate change happening, then one can expect decrease or increase in the global temperature. If there is increase in temperature then one can expect changes in the hydrological pattern in terms of floods, droughts, etc. Any of these extremes do have an impact on the wetlands, and they may even destroy the wetland ecosystem.
Dear Dr. Kenneth, I definitely agree with your observations. I do feel there was climatic VARIATIONS in the past, it will continue be so in the future too. I know that there is weather cycle of hot and cold seasons in any given year. May be I didn't make my point clear in the above answer. What I meant is "if there is global climate change which is as anticipated or projected by the proponents on this debatable issue", then there will be associated problems to wetland ecosystem. Thank you.
For a long-term perspective, see: https://www.researchgate.net/publication/242241344_Carbon_Sequestration_in_Western_Canadian_Peat_Highly_Sensitive_to_Holocene_Wet-Dry_Climate_Cycles_at_Millennial_Timescales
Article Carbon Sequestration in Western Canadian Peat Highly Sensiti...
You can check out Karsten Schittek's work regarding high-altitude wetlands in the Andes, such as https://pdfs.semanticscholar.org/5e95/f36ee8d4beb5df1c06ae3ce806e211287049.pdf. His PhD dissertation is very useful as well: http://www.schweizerbart.de/publications/detail/isbn/9783443643256/%23
In my opinion, having worked with wetland issues for many years, substantial changes in rainfall amount and distribution would have to occur to change a wetland to a non-wetland. Through history, man has gone out of his way to drain them. Historically, some believed wetlands were evil, possibly due to stagnant water, mosquitoes, snakes, etc. Most wetlands are going to be safe unless man drains them, or in some instances prevents the infrequent natural fire that may be needed to keep them as a wetland. Some wetlands have hydric soils, plants and hydrology, but are difficult to classify without site evaluation of the specifics.
Unless there are significant shifts in climate, I believe most wetlands with hydric soils to be safe. There are some soil types such as Leon with spodisols, where the site has wetland characteristics in wet years, and non-hydric soil character in dry years. These type wetlands may be subject to change in their wetland function.
In working on the National Forests in South Carolina with Jason Jennings, USFS soil scientist, we have access to LiDAR coversge and have found many examples of wetland drainage where efforts to recover their hydrology were and are being undertaken. If you are concerned about wetland habitats and functions, recovery efforts is a very viable approach to consider if you can find the old ditches that drained them. Creating wetlands is more difficult.
Climate cannot explain all the change in wetlands. As Kenneth M Towe has said climate has always changed and will change. The current state of the wetlands is the results of the sum of all former environmental changes including the changes in the climate. I prefer to see wetlands as hydro-morphological systems. Climate provides water but geomorphology is what create the conditions for water to be retained. what is really affecting wetlands is the land cover change that is affecting runoff, the movement of the sediments, etc...