By Dr. Norm Catto
How much of ongoing climate change is due
to people? How do we know that we contribute at all?
Current discussion about climate change is based on differences
of scientific opinion concerning both the significance and
magnitude of the changes recorded in temperature and precipitation
statistics, as well as on the “global” nature
of the change, and the appropriateness of applying records
from one region to another. One must always remember that
the discussion of climate deals with long-term averages, over
several decades. The weather for each individual day, month,
season, and year will continue to vary within that overall
In the scientific community, the discussion centres around
whether human activity is responsible for all of the climate
change in the past 150 years, or only for part of it, or if
it is dominantly natural in origin. Scientists agree that
climate change is happening, as it has since the origin of
Earth 4.6 billion years ago, but we’re not all in agreement
as to exactly how much blame should be put on our species,
and how much of the change is natural.
The suggestion that humans are responsible for at least a
significant component of climate change comes from several
lines of evidence. Theoretical considerations suggest that
discharging carbon dioxide and methane into the atmosphere
will cause atmospheric warming, as can be directly observed
above all cities in the developed world where energy use involves
burning fossil fuels. Measurements of carbon dioxide and methane
preserved in ice cores from Antarctica and Kallaallit Nunaat
indicate that the concentrations have been relatively stable
over the past 10,000 years. However, since 1800, the concentration
of carbon dioxide in the ice and the atmosphere has increased
by about 30 per cent, and the concentration of methane has
Increases in temperature have also been
recorded in most areas of North America since 1845. In the
Rocky Mountains, glacial recession and tree ring records (dendrochronology)
indicate that glaciers today occupy less area than they did
9,000 years ago. Most of these glaciers have retreated more
within the past 150 years than they had advanced in the previous
9,000 years. This indicates that climate warming and drying
have occurred in this region, and at an accelerated rate since
1845. Similar conclusions have been drawn from studying lakes
in the Canadian Prairies. In Canada as a whole, Environment
Canada statistics indicate that six of the eight warmest years
on record (i.e. since Fahrenheit invented the thermometer,
around 1800) have occurred since 1992.
We’re not all in agreement as to exactly how much blame
should be put on our species, and how much of the
change is natural.
Unfortunately, these statistics are limited in their usefulness
by the relatively short time that they represent. The longest
accurate temperature records, from Europe and New England,
span the period since Fahrenheit’s thermometer was considered
to be sufficiently reliable – less than 200 years. In
most areas of western North America, accurate temperature
records encompass 150 years at most; in arctic Canada, reliable
observations date from the Second World War. Climate, by definition,
involves long term averages. If climate change is to be recognized,
it is necessary to look beyond the numerical records.
Climate changes in the historic past are assessed by studying
human records based on climate-dependent human activities.
Among those studied are the dates of annual grape harvests
from European Monasteries; the timing of cherry blossoms at
Shinto temples in Japan; the success or failure of wheat cultivation
in the North Atlantic regions; iceberg numbers and time of
ships’ encounters off Iceland’s coast; and trapping
data from the Hudson’s Bay Company. All of these human
activities can be used as analogies to calculate the climate
at those times.
For earlier periods, or in areas where there are no written
records available, proxy data from natural systems are used.
Proxy data are those that can be used to infer climate. Among
the styles of proxy data used to assess past climates from
4.6 billion years ago to 1800 AD are ice core records from
continental and mountain glaciers; pollen analysis from lake
sediments; other microfauna and flora, including diatoms,
insect remains, and marine plankton; dendrochronology; glacial
advances and retreats; changes in ranges of animal and plant
species; changes in soil development and type; and changes
in the types of sediments or landforms, such as glacial features
and sand dunes.
In the countries surrounding the North Atlantic Ocean, abundant
proxy data exists for the last 1,000 years. This recorded
data, along with the impressions of contemporary writers,
allows reconstruction of the climate patterns. The results
show that much regional variability existed, even over very
short distances: adjacent mountain valleys record different
responses to the same weather and climate events. This should
not be surprising, as modern weather events produce equally
diverse responses and effects. When results are compared across
the expense of western Europe and mid-latitude North America,
however, a pattern of consistent climate change emerges.
In general, the period from about 700 to 1300 A.D. was marked
by relatively warm conditions (generally, slightly less warm
than those at the end of the 20th century). This interval
is referred to as the Little Climatic Optimum or the Mediaeval
Warming. Following this, temperatures cooled, resulting in
glacial advances in alpine areas. This event, referred to
as the Neoglacial or Little Ice Age, persisted until the mid-19th
century. The Neoglacial was followed by a cycle of climate
warming, which is currently in progress.
Proxy data, historical records, and numerical temperature
and precipitation observations allow comparison between what
has happened under the purely natural circumstances that undoubtedly
existed prior to 1800 AD, and what has happened since then.
The most striking difference is not in the type of climate
changes, or the areas of occurrence, or the consequences to
organisms: it is the speed at which the changes are occurring.
Changes that required hundreds, thousands, or tens of thousands
of years in the natural and geological records are now seen
within the span of decades. The rates of climate change are
increasing, along with increased human production of carbon
dioxide and methane. The acceleration of the rate of change
began in the early 1800s, just as human consumption of fossil
fuels increased. Ongoing climate changes directly above cities
are proportionate to the amount of energy consumed by each,
with differences evident due to city size, lifestyle, and
economic wealth. Taken all together, the acceleration of climate
change cannot be explained solely by natural causes: human
activity is the only factor that has changed substantially
in Earth’s climate system since 1800.
So, we are not responsible for all climate change: natural
factors continue to operate, as they have for 4.6 billion
years. However, the accelerated rate indicates that humans
have made a contribution in the past 200 years.
Regardless of the cause, however, impacts of climate change
are happening today, and we will all have to adapt. Considering
our resilience in the face of the province’s traditional
weather, we should be able to cope with that in the future.
Dr. Norm Catto has been with Memorial's Department of
Geography since 1989. His research and teaching interests
include the impacts of climate change, and the necessary adaptations,
in Newfoundland and Labrador, throughout Canada, and in Russia.