Veteran Denver broadcast meteorologist Mike Nelson outlines his views on human-caused climate change and does so ‘at some peril’ given the pushback he frequently encounters. Reposted with light edits and with permission of the author.

My thoughts on Climate Change.

Extreme drought, destructive wildfires, tornado warnings at night in Denver, the warmest June and July on record, a new record for the number of days over 90 and 100 degrees — are these random events or are they related to global warming?

The answer is not as easy as a simple yes or no, but overall the answer appears to be a carefully qualified yes. It is complicated and controversial, but I am going to give you some background from my perspective after nearly 50 years of being a “weather nut”. Yes, I have been fascinated by weather and climate since grade school.

Proceeding with Caution

I address this topic at some peril. In many ways, the job description for the TV “Weathercaster” is to simply be the nice friendly person who tells you what the high was, how much rain will fall and what to expect next weekend. Especially in recent years, broaching the topic of global warming can stir up deep emotions within viewers and can bring some rather rough responses via e-mail and Facebook.

Over the course of time, I have been called many different things while talking and writing about this subject. From courageous to foolish, to “the Pied Piper of Anti-Science.” I appreciate the fact that my viewers have many differing views and opinions on many issues, and climate change is one topic that seems to bring a strong reaction.

Nonetheless, TV meteorologists are often asked to provide their viewers with insight and explanations on earthquakes, meteors and comets, tsunamis and volcanoes. For many Americans, we are as close to a scientist as they will get, and they invite us into their living rooms.

They may not agree with my comments and explanations, but I hope they will appreciate the attempt and still choose to watch my weather reports.

So, with that said, here we go.

Weather is NOT Climate

It is very important to realize that a heat-wave, tornado outbreak, record flood or major blizzard is not climate — it is weather. The weather goes through tremendous fluctuations from day to day and even hour to hour — let alone over the course of weeks, months, or even years.

These weather changes have been happening for millions of years and will continue for millions more. Nonetheless, we are now seeing trends consistent with a warming Earth. Experts at the National Center for Atmospheric Research (NCAR) feel that 90 to 95 percent of what we see in the wide variety of weather is caused by natural variability. The remaining 5 to 10 percent is attributable to the warming of the planet as a result of an increase in various greenhouse gases.

A good analogy: Consider the impact of steroid use by a professional athlete. The talent and work ethic of the athlete is responsible of 90-95 percent of what we witness on the playing field. The added “juice” of the steroid accounts for that extra power that can result in faster times or more home runs.

Of course, 5 to 10 percent may not seem like much, but consider what that can mean in terms of tangible measurements. A 5 to 10 percent drop in crop yields over the long haul would have a huge impact on agri-business in our state and across the nation. A 5 to 10 percent drop in snowpack in future decades would be a major concern for Colorado and the West. A 5 to 10 percent increase in insurance losses from weather would amount to billions of dollars over the long term.

Climate Change and Extreme Weather are Linked

Even though an individual severe weather event cannot be blamed on global warming, a warmer climate “juices” the atmosphere and should bring more frequent severe weather events in the future.

Climate Central provides useful insights on how global warming may impact conditions around the world, across the nation and in Colorado.

Warmer average temperatures in the western United States will likely result in more drought and fire concerns in the decades to come. Because we are far away from large bodies of water, higher temperatures here are not usually associated with increased humidity — in fact, just the opposite.

With a gradual warming of the planet, our regional climate is likely to become drier on average over the next 100 years. The result will be more wildfires, lower reservoirs, and more frequent droughts.

Altered El Niño and La Niña Episodes

Periodic warming and cooling of the Pacific Ocean along the Equator has enormous implications on global weather. Scientists do not fully understand the cycles and strength of these events, and they obviously have occurred naturally for a very long time. How they may be altered by a warming ocean is going to be the subject of a great deal of future research.

One Cold Winter Does Not Mean There Is No Global Warming

Unusual local weather events — snow in Las Vegas or extreme cold weather in Texas — inevitably raise questions about climate change. But it is important to understand that short-term weather is to climate as one play in a sports event is to the entire season, or perhaps even to the entire history of that sport.

For example, extreme cold and snow in southern locales usually results from a southern bulge in the circumpolar vortex, bringing chilly air down from Alaska and Canada into the lower 48 states. Often, while portions of the lower 48 states are shivering, Fairbanks may be enjoying mild weather for its area. When that vortex drifts back to the north, Fairbanks is very cold again and Colorado may hit 70 degrees in January.

The key here is that we are talking about regional weather events. Things tend to even out — if one area is unusually warm, another is cold. But on a global average, we are seeing a warming of the planet by about 1.5 degrees Fahrenheit since 1900.

But the World Has Not Warmed Since 1998 …

There is an often quoted issue of 1998 being the warmest year and that global temperatures have cooled since that time. This information is misleading. In 1998, the world climate was influenced by one of the strongest El Niño events ever recorded. This pool of very warm Pacific Ocean water bumped global temperatures higher.

Temperatures have remained warmer than the long term average in the years since then — just not quite as warm as that one spike. While regional weather events tend to even out, globally we are seeing indications of an overall warming of the planet.

But in the 1970s, Some Said Earth Was Cooling!

I did my meteorology training at the University of Wisconsin at Madison in the 1970s. At that time, Dr. Reid Bryson, one of the founders of the UW Meteorology Department, was lecturing about the prospect of a “New Ice Age”.

The cause, Bryson theorized, resulted from the increase in tiny particles of smoke and dust during the Industrial Revolution. The increase in atmospheric aerosols would block incoming sunlight like a dirty window. It was from that theory that several magazines ran feature articles about “Global Cooling.” Some express concerns about such this seeming about-face over forty years.

In fact, even at the time, most researchers, including Bryson, felt that the increase in CO2 would eventually offset this “dirty window” effect and the climate would begin to warm. This is an important point, as many anthropogenic global warming (AGW) skeptics still bring up the “1970s Global Cooling Theory” as an argument that the current consensus among climate scientists has been an “about face” form the 1970s. This view is rejected by authors of an article in the Bulletin of the American Meteorological Society and elsewhere.

What about the Hacked 2009 E-Mails?

The release of private e-mails from the University of East Anglia in late 2009 raised some questions about a hidden agenda among some of the leading climate scientists around the world. The timing of the release of those e-mails came just before the International Climate Conference in Copenhagen clearly diverted the focus of the agenda of that conference.

But of the roughly 60 megabytes worth of e-mail exchanges released, only a small fraction of the private comments truly raised any concerns. Scientists, like other people, often speak casually among themselves in a short-hand of sorts common to their field. In this respect, saying something such as “the trick in this problem” does necessarily mean an actually “trick” or sleight of hand, but rather a method of conducting a calculating. It may not sound good when clipped out of context, but that’s about it. Other seemingly questionable comments also were taken out of context to distort their full meaning.

Cherry picking quotes can often be very misleading, and this goes for all sides of any issue. My climate researchers will be emboldened by the e-mails controversy to just “put it all out there.” With a fully open discourse from all sides, maybe we can get past the political wrangling and truly get down to the business at hand. In any event, we will have to make worldwide policy decisions on climate and energy for the generations to come, and there will certainly be a lot of politics in this endeavor.

What about Hurricanes and Typhoons?

There has been a disagreement among some atmospheric scientists concerning impacts of global warming on frequency and intensity of hurricanes. This is a tricky subject as there are many facets to the development of tropical storms and hurricanes.

On the surface, it would seem to make sense that adding energy to the atmosphere would increase the number and strength of these storms. But the situation is more complex than that as changes in the atmosphere may shift wind patterns and ocean temperatures.

These changes are not necessarily going to manifest themselves in more and stronger tropical storms, hurricanes or typhoons. It may well be that these systems become less frequent, but more intense.

However, just because there is some disagreement in regard to individual weather events or seasons, that does not mean that the increased greenhouse gas concentrations are not changing the global climate system.

Remember, weather is not climate, but in the long term, we expect a 5 to 10 percent impact above what we expect from natural variability. This may change the tropical system in ways that we do not yet fully understand.

Periodic Ocean Circulations

Our planet is over 70 percent covered by water, and the oceans play a dominant role in daily weather and in Earth’s long-term climate. There are some very important patterns in the world’s oceans that shift from warm to cool, higher pressure to lower and in their position in the ocean. Two of the most important from weather in the Northern Hemisphere is the Pacific Decadal Oscillation and the North Atlantic Oscillation.

There are several arguments that attempt to refute human-caused or anthropogenic global warming (AGW) that have been pretty well debunked. I will address several more in Part 2 of this re-posting. Some of these arguments are so tired — such as the 1970s Global Cooling or arguments alleging wrong-doing involving the East Anglia e-mails, that we should move on to study issues that really are still a question.

One of the ongoing controversies involves impacts of many of the deep ocean currents and oscillations. These phenomena are complex and hard to fully understand, and it’s an area I find especially intriguing in terms of impacts on future climate. Among the resources I find most useful in keeping abreast of this issue is this NOAA site.

Editor’s Note: This is the first of a two-part reposting, with permission of the author, broadcast meteorologist Mike Nelson of Denver. Part 2 will be posted on April 15.