One key step is to phase in electric power tools as alternatives to fossil fuel powered ones or even give some up. The rotovator, for example, has no place in a climate-friendly garden, which is a relief to many of us and our backs!
Pesticides can also go as they are energy-intensive to produce, particularly glyphosate, the active ingredient in Roundup; the organic movement advises on nature-based alternatives. The same goes for artificial NPK fertilisers, especially in the case of nitrogen, whose production is also extremely energy-intensive.
Ironically many of these nitrate fertilisers are over-applied and easily leached out of soils, when nitrogen can be more readily applied via composts, well-rotted manures and leguminous plants such as peas, beans and clovers. After all, their root nodule bacteria perfected the N-fixing process eons before 20th century industrial processes appeared, with far less fuss and a very much gentler impact upon the environment.
Commercial rock phosphate has to be mined and transported, unlike that supplied by mycorrhizal fungi. Given half a chance, these fungi will invade plant roots and set up a nutrient barter system, with some of the plant’s sugars being exchanged for the much less available and distant phosphates that plant roots can’t normally reach. These weren’t understood by scientists until relatively late in the 20th century, when ploughing, rotovating and agrochemicals had effectively destroyed most of the mycorrhizae in arable soils. Nowadays their reintroduction is being promoted by organisations such as the RHS, although primarily for soils that are not going to be heavily cultivated or fertilised. This seems to be another good reason for giving up the rotovator and adopting a minimum till or agroecological approach, especially since healthy undisturbed soils will already have or acquire their own mycorrhizae.
An important reason for adopting low till systems, reinforced by recent research hot off the press, is that bare soil is vulnerable, not just to erosion and invadin
g weeds but also to carbon loss through exposure to the atmosphere. Where soil has to be exposed between crops, it’s best covered as soon as possible by cover crops or mulches to stabilise it. Many of these cover crops are green manures, which include legumes and deep rooted plants, such as comfrey, which help to recycle nutrients and reduce the need for external inputs.
Planting trees and shrubs wherever possible is an obvious step, especially as trees also provide shade and cool the air via evapotranspiration, but perennials and permanent species-rich grasslands are also important. Recent research in the UK has shown that such grassland can store far greater quantities of carbon in its underlying soils than previously appreciated, particularly with intermediate levels of management, such as limited mowing and feeding.
Finally, we know that all good gardeners compost their crop residues, weeds and kitchen waste. That’s even more important for climate-friendly gardening as the organic matter returned to the garden adds to the below-ground carbon store. Another really neat trick is to add carbon in the form of biochar. 
Produced from woody materials in the same way as charcoal, biochar resists degradation and can hold its carbon in soils for hundreds to thousands of years. Fragments of biochar are fine-grained and highly porous, so when mixed with soil they also help it to retain nutrients and water.
It‘s tempting to describe the use of biochar as a 21st century approach but in reality this is a 2,000 year-old practice as evidenced by biochar-rich dark earths (Terra Preta) found in the Amazon. Most of the other techniques are equally old and well-proven. In effect, 21st century gardening means bypassing the fossil fuel-based methods of the 20th century, the one that accelerated climate change in the first place by divorcing human activity from natural cycles.
Picture credit: Mycorrhizal fungi Trüffel Didi, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons. This file is licensed under the Creative Commons Attribution-Share Alike 4.0 International license. Image cropped to delete foreign language labels.