Humans causing climate change for 180 years: study

Human activity has been causing global warming for almost two centuries, proving human-induced climate change is not just a 20th century phenomenon, a new study has found.
According to the study, warming began during the early stages of the Industrial Revolution and is first detectable in the Arctic and tropical oceans around the 1830s, much earlier than scientists had expected.
"It was one of those moments where science really surprised us. But the results were clear. The climate warming we are witnessing today started about 180 years ago," said Nerilie Abram, associate professor at The Australian National University (ANU).
The findings have important implications for assessing the extent that humans have caused the climate to move away from its pre-industrial state, and will help scientists understand the future impact of greenhouse gas emissions on the climate.

"In the tropical oceans and the Arctic in particular, 180 years of warming has already caused the average climate to emerge above the range of variability that was normal in the centuries prior to the Industrial Revolution," Abram said.
She said anthropogenic climate change was generally talked about as a 20th century phenomenon because direct measurements of climate are rare before the 1900s.

However, the team studied detailed reconstructions of climate spanning the past 500 years to identify when the current sustained warming trend really began.
Scientists examined natural records of climate variations across the world's oceans and continents. These included climate histories preserved in corals, cave decorations, tree rings and ice cores.

The research team also analysed thousands of years of climate model simulations to determine what caused the early warming.
The data and simulations pinpointed the early onset of warming to around the 1830s, and found the early warming was attributed to rising greenhouse gas levels.
Helen McGregor, from the University of Wollongong said humans only caused small increases in the level of greenhouse gases in the atmosphere during the 1800s.
"But the early onset of warming detected in this study indicates the Earth's climate did respond in a rapid and measurable way to even the small increase in carbon emissions during the start of the Industrial Age," McGregor said.

The researchers also studied major volcanic eruptions in the early 1800s and found they were only a minor factor in the early onset of climate warming.
The earliest signs of greenhouse-induced warming developed during the 1830s in the Arctic and in tropical oceans, followed by Europe, Asia and North America, Abram said.
However, climate warming appears to have been delayed in the Antarctic, possibly due to the way ocean circulation is pushing warming waters to the North and away from the frozen continent.
Last year saw the record of maximum temperature - Palakkad
- registering 41.9 degrees Celsius - in the state.

The maximum temperatures recorded in many parts of Kerala either crossed or reached near the critical level of 40 degrees Celsius, leading to unpleasant living conditions.
The report also said climatological analysis of rainfall data for the last 140 years show cyclic pattern with a significant declining trend in the south-west monsoon season for the last six decades.
"Rainfall in June and July shows a decreasing trend while that during winter and post-monsoon shows a slight increasing trend," the report said.
Quoting Indian Meteorological Department (2013) documents, it said the state is witnessing an average decline in South West monsoon rainfall by about 2.42 mm per year.

"Kerala also witnesses an increase in annual mean temperature by 0.01 degree Celsius/year. Most alarmingly, this trend is uniform in all seasons and at all locations of the state," it said.
The State Action Plan on Climate Change has identified four districts- Alappuzha, Palakkad, Idukki and Wayanad- categorised as climate change 'hot spots' in Kerala due to high degree of vulnerability to natural hazards like flood and drought, and impact on biodiversity and human life, the report added.